How to Make a Mattress Softer or Firmer

Make a mattress softer by adding a plush foam or fibre mattress topper, breaking it in through daily use, rotating or flipping it if flippable, and warming the room to relax the foam. Make a mattress firmer by adding a firm high-density foam or latex topper, supporting it with a sturdier bed base, cooling the room to firm the foam up, or sliding a plywood board between the mattress and slats. DIY fixes work best when the mattress is close to the feel you want but not quite right; if the mismatch is dramatic or the mattress is past its useful life, replacement is usually better value than compounding fixes.

Key Takeaways

• The fastest way to make a mattress softer is a plush 5 to 8 cm foam or fibre mattress topper; the fastest way to make it firmer is a firm high-density foam or latex topper of similar depth

• New mattresses often feel firmer for the first 30 to 60 days because the foam is still settling; wait out the break-in period before spending on toppers

• Room temperature directly affects foam feel: warmer rooms make memory foam softer, cooler rooms firm it up

• A sagging or under-supportive bed base can make a mattress feel too soft: slat gaps over 6 cm and broken slats make the mattress feel plusher than it is

• Our Koala Mattress and Koala Plus feature flippable comfort layers with a firmer and softer side built in, so you can adjust feel without buying a topper

How to Make a Mattress Softer

Soften a mattress by adding a plush topper, breaking it in through daily use, flipping or rotating it, and warming the room. Toppers deliver the biggest single change; the other three steps refine feel and can be tried before spending anything.

Step 1, Add a Soft Mattress Topper

A 5 to 8 cm memory foam or fibre-fill mattress topper softens the sleep surface immediately by adding a plush layer above the mattress core. Choose a lower-density memory foam (35 to 50 kg/m³) or a wool/cotton fibre topper for the softest feel; higher-density foam won't soften as much. Fit a fitted sheet over the topper to hold it in place, and expect a topper to last 3 to 5 years on daily use.

Step 2, Break the Mattress In

New mattresses typically feel firmer for the first 30 to 60 days of use because the foam layers are still settling into their final feel. Sleep on it consistently, walk on it barefoot for a few minutes each day, and give the break-in period a proper chance before deciding it's too firm. Our Koala mattresses take 3 to 5 days to fully expand initially and continue softening slightly over the first month or two of daily use.

Step 3, Flip or Rotate It

Rotate your mattress head-to-foot every 3 months to redistribute wear evenly across the sleep surface. If your mattress has a flippable comfort layer (like our Koala Mattress with Firm/Medium-Firm flippable sides, or our Koala Plus with Medium-Firm/Medium flippable sides), flip to the softer side for an instant feel change without spending anything. Check the mattress label or manufacturer instructions to confirm flippability before attempting; some mattresses are single-sided and shouldn't be flipped.

Step 4, Warm the Room Up

Memory foam softens as temperature rises. Raising the bedroom temperature from 18°C to 22°C can make a firm-feeling memory foam noticeably plusher, especially in the first hour of sleep as the foam warms to body temperature. This works best on memory-foam-heavy mattresses (including ones using open-cell foams like our Kloudcell®); latex and pocket-spring mattresses are much less temperature-responsive.

How to Make a Mattress Firmer

Firm up a mattress by adding a firm high-density foam or latex topper, supporting it with a sturdier bed base, cooling the bedroom, or sliding a plywood board between the mattress and slats. Combine multiple fixes if a single one isn't enough, and diagnose the root cause (mattress feel, base support, room temperature) before spending.

Step 1, Add a Firm Mattress Topper

A 5 to 8 cm high-density foam (60 kg/m³ and above) or firm Dunlop latex topper adds firmness above a too-soft mattress core by presenting a firmer surface to your body weight. Firm toppers are less common than plush ones on the AU market; look specifically for high-density polyurethane (HR grade or higher) or Dunlop latex, and confirm the density figure before purchase. This is the least invasive firmness fix.

Step 2, Support It With a Sturdier Base

A soft-feeling mattress can be caused by inadequate support underneath, not the mattress itself. Check the bed base: slats should be no more than 6 cm apart for foam mattresses, and slats should be flat and unbroken. A slatted base with wider gaps or broken slats can make a mattress feel much softer than it actually is. Consider a solid platform base or our wooden bed base and frames for consistent, even support that lets the mattress deliver its designed firmness.

Step 3, Cool the Room Down

Memory foam firms up as temperature drops. Cooling the bedroom from 22°C to 18°C can make a soft-feeling memory foam noticeably firmer, especially in the first hour of sleep as the foam sets. This works best on memory-foam-heavy mattresses (including Kloudcell® builds); latex and pocket-spring mattresses are less temperature-responsive.

Step 4, Slide a Board Underneath

A 12 to 18 mm plywood board cut to fit between the mattress and the slats adds immediate firmness by removing the flex of the slats. This is a temporary fix useful for testing whether firmness will actually solve the problem before buying a new mattress or topper. Not recommended as a long-term solution because it reduces airflow through the mattress base and can cause moisture build-up over time.

Softer vs Firmer Fixes at a Glance

The following table consolidates both softening and firming fixes with cost, timing, and best-fit scenario. Use it as a diagnostic: match the fix to your problem before committing to the cost.

Start with free fixes (break-in, flip, temperature) before spending on toppers or bed bases. If free fixes don't shift the feel enough, a topper is usually the best next investment because it can be reused on a future mattress.

When a DIY Fix Won't Work Anymore

DIY fixes won't work when the firmness mismatch is dramatic, when the mattress is past 8 to 10 years of daily use, when there's visible structural damage (broken springs, cracked foam, visible sag greater than 3 to 5 cm), or when a warranty replacement is available. In these cases, replacement usually delivers better value than compounding fixes that only delay the inevitable.

Signs it's time to replace, not fix:

• Mattress is past 8 years of daily use (or 5 years for a budget mattress); toppers only delay replacement

• Visible sag greater than 3 to 5 cm in the sleeping area; toppers can't compensate for structural mattress failure

• You've tried a topper and the problem persists; the mismatch is bigger than a topper can address

• You wake up with back or neck pain multiple mornings a week; a mattress mismatch is a health issue, not just a comfort preference

• Warranty replacement is available (our Koala mattresses come with a 10-year warranty; check terms if your current mattress qualifies)

• The mattress is a fundamentally different firmness than you need; a firm mattress "softened with a topper" is still fundamentally firm underneath

If you're at the replacement point, our Koala range includes flippable options with two firmness settings built in, so you can dial in the right feel without needing to buy a topper on day one.

Explore Our Flippable Mattress Range with Built-In Firmness Options

Our Koala mattress range includes flippable mattresses with two firmness options built in, so you can adjust feel without a separate topper. All feature Kloudcell®, a durable, high-density open-cell foam, plus CertiPUR-US® certified foam, Zero Disturbance® technology, our 120-night trial, and 10-year warranty. Explore the range:

• Koala Mattress: the flippable Firm/Medium-Firm original, 25 cm total height with 7 cm Kloudcell® (40% more than SE), zip-off topper with carbon-zero TENCEL™ Lyocell ticking, and 3-zone charcoal marble dyed support. Flip between the two firmness sides depending on your preference.

• Koala Plus Mattress: flippable Medium-Firm/Medium, 28 cm total height with 8 cm Kloudcell® (60% more), Cooling Gel Kloudcell® flippable comfort layer, reversible summer/winter topper, and 5-zone support with bamboo charcoal edge support.

• Koala SE Mattress: Medium firmness (non-flippable), 23 cm total height with 5 cm Kloudcell® and TENCEL™ Lyocell breathable cover. Our entry option.

Browse our full premium mattress range for all firmness options, or explore our wooden bed base and frames since sturdier support can change how firm your existing mattress feels.