Does Mattress Thickness Matter? What Actually Decides Support and Feel

Why are mattresses so thick now?

Every mattress is built in two parts. The support core at the bottom is the spring unit (Bonnell or pocket spring) that holds your weight up. The comfort layers on top are the quilting, foams, memory foam or pillow top that decide how the surface feels when you first lie down. Add the cover and base panel, and that is the total height on the label.

Modern mattresses have grown taller because makers add deeper spring units, more comfort layers or both, and a tall profile looks generous on a showroom floor. But height on its own says nothing about which part grew. Here is how six mattresses from our range break down, with the feel each one's product page gives it:

Two things stand out. First, the spring core is most of the height in every one of them; everything else, from the comfort layers to the cover, adds between 1 cm and 10 cm. Second, the tallest mattress here is one of the softest, and the two 30 cm mattresses feel different: one plush, one medium. Height and feel are simply not linked.

Does a thicker mattress feel more supportive?

Not because it is thicker. Support comes from three things in the core:

• Spring type. Bonnell springs are linked together as one unit, giving a firm, even base. Pocket springs are individually wrapped, so each one moves largely on its own rather than as one connected unit. Our guide to pocket spring mattresses explains the difference.
• Wire gauge. Thicker wire makes a stiffer spring. The Posture Delight's 2.3 mm wire is one reason it feels firmer at 28 cm than the Chill Sleep, whose pocket springs use 1.9 mm wire, does at 34 cm.
• Zoning. A five-zone core, as in the Spine Care, Cradle Rest and Supreme Care, tunes the support along the length of the body. In the Supreme Care it is firmer through the middle, with a little more give at the shoulders.

The comfort layers then set the surface feel: how soft the first few centimetres are, and how much you sink in. A deep comfort stack makes a mattress feel plusher, not more supportive. A thin, well-built pocket spring mattress can feel steadier underneath than a taller one with a soft core.

So when a thicker king or queen feels more supportive in the showroom, check why. It may have a firmer wire, zoning or a denser foam, and those are the things worth paying for. If the extra height is all soft foam, it is mostly a feel choice.

How thick should a mattress be?

Pick the build for the bed's job, then let the height follow:

• Bunks, trundles, kids' rooms and guest beds: a slim mattress around 18 to 20 cm is usually right. It keeps the bed low, it is lighter to lift when you change the sheets, and on a bunk it keeps the guard rail above the mattress. Always check the bunk maker's maximum mattress thickness. Browse our thin mattresses, or compare the 20 cm Sleep Essential III with the 19 cm Sleep Rest Bonnell Spring Mattress.
• An everyday adult bed: the mid-range pocket spring builds in this guide sit between 26 and 30 cm, but choose them on core and feel. The Spine Care 5 Zone Pocket Spring Mattress at 26 cm and the Cradle Rest at 30 cm both have five-zone cores, and both product pages label them Medium, 5 out of 10.
• A plush, cushioned surface: look for deeper comfort layers or a pillow top. Browse our pillow top mattresses; the Sleep Vital Pillow Top Mattress, for example, is 23 cm tall and adds a pillow top and 3.5 cm of high-density foam over Bonnell springs.

Is a 20 cm mattress good?

For a guest room, a child's bed or a bunk, yes. The Sleep Essential III is 20 cm and still has an 18 cm pocket spring core. For a main bed shared by two adults, most people prefer a little more comfort layer on top, so lie on a few heights and compare.

Check the total bed height

A 34 cm mattress on a tall base can leave the top of the bed higher than you expect. Add the mattress height to the base height, then sit on the edge in the showroom: your feet should rest flat on the floor. Tall mattresses also need fitted sheets with a deep enough pocket.

Thickness and your sleeping position

Your sleeping position matters far more than the tape measure. We group our mattresses into four collections, Soft & Plush, Medium Firm, Firm and Extra Firm, and each product page also gives its own feel label and a score out of 10. As a starting point:

• Side sleepers usually suit Soft & Plush or Medium Firm, because the shoulders and hips need room to sink in. That cushioning comes from the comfort layers, so a side sleeper may like a taller comfort stack, but a slimmer soft mattress can do the same job.
• Back sleepers usually suit Medium Firm, or Firm for heavier builds.
• Stomach sleepers usually suit Firm, so the hips do not dip.
• Couples and combination sleepers often meet in the middle at Medium Firm.
• Heavier builds usually go one tier firmer, and should look for a sturdy core rather than extra soft foam on top.

For the full breakdown, read our sleeping positions and mattress firmness guide.

Other mattress myths worth dropping

• "Firmer is always better." The right firmness depends on how you sleep and your build. Too firm can feel hard at the shoulders and hips, just as too soft can let you sink.
• "You have to flip your mattress." Most modern mattresses, including the Supreme Care, Posture Delight and Chill Sleep, are single-sided with the comfort layers on top. Rotate them head-to-foot every few months instead.
• "More springs means a better mattress." Spring counts rise with size: the Supreme Care has 660 pocket springs in queen and 810 in king. Compare counts only at the same size, and weigh them against wire gauge, zoning and comfort layers.
• "A topper will fix a tired mattress." A topper changes the surface feel, but it cannot replace support that the core no longer gives.

Feel is personal, so the surest test is to lie on a few mattresses in your usual sleeping position. We have five showrooms (Rocklea, Virginia, North Ipswich, Bundall and Beenleigh); ask which store has the mattress you want on display. You can also see current offers in the mattress sale.

Mattress thickness FAQs

• Are thicker mattresses more comfortable?

  Not automatically. Extra height usually means more comfort layers, which can feel plusher, but comfort depends on whether the feel suits your sleeping position and whether the core supports you. A well-matched slimmer mattress can be more comfortable than a taller one.

• How thick is a memory foam mattress?

  It varies, and the memory foam is often only one layer. In the mattresses in this guide, memory foam sits on top of pocket springs: the Chill Sleep has a 2 cm gel memory foam layer in a 34 cm mattress, and the Supreme Care has memory foam in its quilted top on a 30 cm mattress.

• Is a heavier mattress better?

  Not on its own. Weight follows the size and the materials, so a bigger or taller mattress weighs more without being better made. Judge a mattress on its core, wire gauge, zoning and comfort layers instead.

• Does a bigger mattress size mean a thicker mattress?

  No. Each mattress in this guide has one total height across all its sizes, so a single and a king of the same model are equally thick. Size changes the width and length only.

• Can a mattress be too thick?

  Yes, for some beds. A very tall mattress can make the bed awkward to sit on and get out of, it can sit above a bunk's guard rail, and it needs deep-pocket fitted sheets. Check the total height of mattress and base before you buy.

• What is the average mattress thickness?

  There is no single standard. The mattresses in this guide run from 18 cm to 34 cm, with slim builds for guest and kids' beds at the low end and most of the pocket spring builds between 26 and 30 cm.