Available 
Rock Hard Super Firm Foam Mattress
from £254-£458.
£254-£458
Sizes tracked: Single, Small Double, Double, King Size, Super King
Sleep guide
How to choose a firm mattress without buying the wrong feel
Compare firm and extra firm mattresses in Mattress Online’s own scale, then narrow the choice by sleep position, construction, depth and trial terms.
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Last verified: 2026-09-01
What 'firm' actually means
Mattress Online says firmness is personal, and that there is no universal right or wrong choice. It also uses its own 1-to-5 firmness scale rather than an industry-approved label, so one brand’s firm can feel different from another’s. On this shortlist, the Rock Hard Super Firm Foam Mattress, Rock Hard Ultra Firm Mattress and Premium Gold 2000 Pocket Extra Firm Mattress show how a firm feel can come in different constructions and price points, so the real comparison is how much give you want, not just the word on the page.
Who usually suits a firm mattress
The wider buying guidance points to back sleepers and front sleepers as more likely to suit a firmer surface, especially if they prefer a steadier, more supportive feel. Side sleepers may need more cushioning at the shoulders and hips, so a very firm bed can feel too rigid for some people even when it looks like a good value. If you share a bed, it is worth checking whether both sleepers want the same level of support before choosing between firm and extra firm.
Firm vs extra firm vs medium-firm
Within Mattress Online’s own wording, firm still has some give, while extra firm feels more rigid with less cushioning. That makes the Rock Hard Ultra Firm Mattress and Premium Gold 2000 Pocket Extra Firm Mattress useful comparison points if you want a distinctly harder feel, while the Rock Hard Super Firm Foam Mattress sits between construction and comfort-language cues that may suit shoppers who want firmness without going all the way to the most rigid end. If you are unsure, compare firm against extra firm first rather than assuming all firm-labelled mattresses will feel similar.
How to check online firmness before you order
Because firmness is hard to judge from a product page alone, look beyond the label and check the construction, depth and size range. The Rock Hard Super Firm Foam Mattress is shown as 23cm deep, single-sided and rolled up, while the pocket sprung Premium Gold 2000 Pocket Extra Firm Mattress uses pocket springs and the Ultra Firm model uses reflex foam, so each one will handle support differently. Depth matters too, because it can affect bedding, toppers and bed-frame compatibility, so always recheck live product details before buying.
What matters most from the shortlist
The strongest shopping signals here are practical, not technical. The three example mattresses all show a 100-night comfort trial, which helps reduce the risk of ordering online when firmness is difficult to judge in advance. The visible star ratings are 4.7 for the Rock Hard Super Firm Foam Mattress, 4.6 for the Rock Hard Ultra Firm Mattress and 4.5 for the Premium Gold 2000 Pocket Extra Firm Mattress, but review volumes are not supplied here, so those scores should be treated cautiously. Price spans also matter: the Super Firm Foam model runs from £254-£458, the Ultra Firm from £244-£478 and the Premium Gold 2000 Pocket Extra Firm from £289-£609, so this is more of a value-and-fit comparison than a straight like-for-like ranking. The guarantees differ too, at 10 years, 3 years and 1 year respectively, which is useful context when comparing peace-of-mind features.
How to choose between these firmer options
If you want the most rigid feel, start with the extra firm options and then decide whether you want foam or pocket sprung support underneath. The Rock Hard Ultra Firm Mattress is the lowest entry price in the trio at £244-£478, while the Premium Gold 2000 Pocket Extra Firm Mattress is the highest-priced at £289-£609 and adds a pocket sprung build plus a Small Single size, so it may suit different space and comfort needs rather than a single budget buyer. The Rock Hard Super Firm Foam Mattress adds a 23cm depth, a 10-year guarantee and a rolled, single-sided design, which may appeal if ease of setup and longer guarantee cover matter more than choosing the hardest possible feel. All three show free delivery on the product tiles, but you should check the retailer for latest price and availability before ordering.
Mattresses to use as comparison examples
Available 
Rock Hard Ultra Firm Mattress
from £244-£478.
£244-£478
Sizes tracked: Single, Small Double, Double, King Size, Super King
Available 
Premium Gold 2000 Pocket Extra Firm Mattress
from £289-£609.
£289-£609
Sizes tracked: Small Single, Single, Small Double, Double, King Size, Super King
Retailer details used
Last checked 2026-09-01. The source list below is included to help you check the details behind the comparison. Always confirm the latest price, delivery cost, stock status and product details with the retailer before buying.
- Rock Hard Super Firm Foam Mattress | MattressOnlineproduct-page evidence for Rock Hard Super Firm Foam Mattress
- Rock Hard Ultra Firm Mattress | MattressOnlineproduct-page evidence for Rock Hard Ultra Firm Mattress
- Premium Gold 2000 Pocket Extra Firm Mattress | MattressOnlineproduct-page evidence for Premium Gold 2000 Pocket Extra Firm Mattress
- Firm Mattresses - 100-Night Trial - MattressOnlineFirm mattress suitability, firmness definitions, construction types, trial mention
- What Mattress Firmness Is Right for Me? | MattressOnlineRetailer firmness scale, non-standardized ratings, personal choice framing
- How to Make a Mattress Firmer – 10 Easy Steps | MattressOnlineFirmness vs support, body shape/sleep position caveat, back pain caution
Helpful next reads
Use these related mattresses guides and reviews to turn the advice into a practical shortlist.
Firmness questions
Is a firm mattress always the right choice?
No. Mattress Online says firmness is personal, and the better choice depends on sleep position, body weight and how much cushioning you want. A firmer mattress can suit some back and front sleepers, but it is not automatically the right answer for everyone.
What is the real difference between firm and extra firm?
Extra firm usually feels more rigid and less cushioned, while firm still has a little more give. On this page, the Ultra Firm and Premium Gold 2000 Pocket Extra Firm models are the best comparison points if you want to feel how that difference affects comfort and support.
Are very firm mattresses suitable for side sleepers?
Sometimes, but many side sleepers need more cushioning around the shoulders and hips than a very firm mattress provides. If you sleep on your side often, look carefully at the product construction, not just the firmness label, and use the 100-night comfort trial as a safety net.
Why does mattress depth matter for bedding and bed frames?
Depth can affect how well sheets, toppers and the mattress fit on your base or frame. The Rock Hard Super Firm Foam Mattress is listed at 23cm deep, so it is sensible to check the live product page and compare that figure with your current bedding and bed-frame clearance.
How do trial periods and guarantees help when buying online?
A 100-night comfort trial gives you some room to judge whether a firm feel is right in your own bedroom, which matters because firmness is subjective. Guarantees differ across the shortlist, so compare them alongside construction and price rather than treating them as a substitute for comfort fit.