Firm vs Medium vs Soft Mattress: How to Choose the Right Firmness

Why Firmness Matters More Than Brand

What actually determines whether you wake up refreshed or sore is firmness relative to your body. A mattress rated medium-firm by the manufacturer might feel firm to a 55kg person and soft to a 100kg person.

The Firmness Scale Explained

Soft (1-3): Deep sinking, maximum contouring. Best for lightweight side sleepers under 65kg.

Medium-soft (4-5): Noticeable contouring with some support beneath. Good for average-weight side sleepers.

Medium-firm (5-7): The most universally comfortable range. Suits most body types and sleep positions.

Firm (7-8): Minimal sinking. Strong pushback. Best for back sleepers, stomach sleepers, and heavier individuals over 90kg.

Extra-firm (9-10): Very little give. Rarely recommended unless specifically preferred.

Matching Firmness to Sleep Position

Side sleepers need softer surfaces (4-6) because the shoulder and hip protrude further.

Back sleepers need medium-firm (5-7) to support the lumbar curve.

Stomach sleepers need firmer surfaces (6-8) to prevent the pelvis from sinking.

Combination sleepers need medium (5-6) for versatility across all positions.

Body Weight and Firmness

Under 65kg: Choose one firmness level softer than the general recommendation.

65-90kg: Standard firmness recommendations apply.

Over 90kg: Choose one firmness level firmer. Also look for thicker support layers.

The Firmness Mistake

The most common mistake is buying too firm. Research consistently shows medium-firm outperforms firm for pain relief and sleep quality across most body types.

How Claire Handles Firmness

When you tell Claire your sleep position, body type, and any pain points, she maps these to an ideal firmness range and scores every mattress in the DOME index against that range.

This content is educational only and not medical advice.

## What Firmness Numbers Actually Mean

Mattress firmness is a rating of how the surface resists your body — not a measure of quality. A firm mattress resists compression and keeps the body near the surface; a soft mattress sinks under you; medium sits between. The scale most Australian retailers use runs 1-10, with around 6-7 labelled 'medium-firm', and the exact feel varies by brand, so the number is a starting point, not a fact.

Firmness experiences are body-weight dependent. A 55kg side sleeper can feel a 'medium-firm' as genuinely firm, while a 100kg sleeper can sink through it. Always think of firmness in relation to your own weight and sleep position, and test in the position you actually sleep in.

## Matching Firmness to Sleep Position

Side sleepers need softer support at the shoulder and hip because those bony points press deepest; medium to plush builds relieve that pressure, while an over-firm mattress causes shoulder pain and tingling arms. Back sleepers need medium-firm to support the lumbar curve without sinking the hips. Stomach sleepers need the firmest support to stop the hips sinking and the spine arching.

When in doubt, buy medium-firm. It is the most versatile single choice: it supports back and stomach sleepers acceptably and works for side sleepers in the mid-weight range. A topper is a cheaper way to adjust firmness down (soften) than a new mattress is to adjust it up.

## The Five-Minute In-Store Test

Testing a mattress properly takes more than a sit-down. Lie in your dominant position for at least five minutes, relax the muscles, and check three things: pressure at the shoulder or hip (side sleepers), the feel of the lumbar gap being filled (back sleepers), and whether your hips sink before your chest (stomach sleepers). Move around briefly to see how hard repositioning is — a mattress you sink into is also one you struggle to move in.

Bring your typical sleep partner's weight into the decision too: a couple should both test the same mattress, since the heavier sleeper determines the support requirement.