Mattress Online Rock Hard Super Firm Foam Double Mattress
The Rock Hard Super Firm Foam Mattress from Mattress Online does exactly what the name suggests.
- Very firm, full-height foam build
- Helps keep your spine aligned
- 100-night trial & 10-year guarantee
£334
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Mattress Online Rock Hard Super Firm Foam Mattress
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Mattress details
Mattress
Mattress Online Rock Hard Super Firm Foam Mattress
Size
Firmness
Firm
Construction
Foam
Orthopaedic
Depth (cm)
23
Layers
Layer Details
Reflex Foam
A supportive foam that moulds to your body, which means it promotes spinal alignment and a slightly personalised feel despite the very firm surface. It's durable and resilient, holding its shape for an extended period of time.
Layer details from mattressonline.co.uk product page, September 2026.
Key benefits
- Room to share without crowding the room: At 135 x 190cm, the UK double fits comfortably in most UK bedrooms, leaving space for wardrobes and drawers where a UK king would dominate.
- 67.5cm each for couples: Two people sharing get 67.5cm of width apiece, which on a very firm, stable surface means you each stay on your own side rather than rolling together.
- Firm support across the full width: The 23cm reflex foam build feels solid edge to edge, so neither sleeper drifts into a soft spot when you spread out.
- Bedside tables on both sides: Allow at least 2.6m x 2.8m and most rooms will still take a table each side, useful when you both want a lamp and a phone within reach.
- Easy to dress on any budget: Double sheets and 200 x 200cm duvets are sold everywhere at every price, handy if you're kitting out a whole home at once.
This size suits you if...
You share the bed every night and both want a very firm feel, perhaps on medical advice, in a room that couldn't comfortably take a UK king. It also suits a solo sleeper who likes space to stretch out, or one who shares with a dog or cat that claims a corner. And it works well in a guest room that hosts visiting couples a few times a year.
Consider another size if...
You and your partner both like to spread out, or one of you is a restless sleeper who needs distance. We'd recommend the UK king instead: it gives 75cm each, 7.5cm more per person, and needs a room of at least 2.7m x 2.9m.
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FAQ's
Is the Rock Hard Super Firm double big enough for a couple?
Yes, for most couples. The UK double gives 67.5cm of width each, and because the reflex foam is very firm and stable you won't roll towards each other in the night. That said, if either of you is broad-shouldered or sleeps restlessly, the UK king's 75cm each is a meaningful upgrade.
What size room do I need for the Rock Hard double mattress?
We suggest at least 2.6m x 2.8m, with around 3m x 3m the comfortable norm. That guidance is ours, not the manufacturer's. At the minimum you'll still walk round the bed; at the comfortable size you can add bedside tables on both sides and open wardrobe doors freely.
Will a very firm foam mattress in a UK double suit two sleepers of different weights?
Better than most sizes and feels would. The extra-firm reflex foam barely dips, so a heavier partner won't create a slope the lighter one rolls into. The trade-off is that a lightweight side sleeper may find it too unyielding at the shoulder and hip, whatever the size.
Is the double version of the Rock Hard mattress heavy to move?
The 23cm solid foam build makes this a substantial mattress, and at 135 x 190cm rotating it is realistically a two-person job. If your home has a turning staircase in an older terrace or a tight new build landing, measure the route before ordering, as a foam slab this firm doesn't flex much.
Should I get the Rock Hard mattress in a double or a king?
Choose the UK double if your room is around the 2.6m x 2.8m mark or you want the widest choice of affordable bedding. Choose the UK king if you have at least 2.7m x 2.9m and want the extra 15cm of width and 10cm of length; taller sleepers will notice the length most.