Sealy PostureTech Alderney Super King Mattress
The Sealy PostureTech Alderney Mattress combines twice-tempered PostureTech springs with a MemorySense foam layer, which means firm, responsive support with some pressure-relieving cushioning on top.
- Firm, supportive feel
- Pressure-relieving foam on top
- Edge-to-edge support across the bed
£699
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Sealy PostureTech Alderney Mattress
More available sizes
Mattress details
Mattress
Sealy PostureTech Alderney Mattress
Size
Firmness
Firm
Construction
Foam
Memory Foam
Depth (cm)
Layers
3
Layer Details
MemorySense foam layer
A pressure-relieving foam that Sealy says instantly cocoons your body. It gives the firm mattress some cushioning where you need it.
Responsive foam layer
An additional layer of responsive foam that Sealy says enhances comfort. It adds a little more padding to the feel of the mattress.
PostureTech Core Support springs
Twice-tempered PostureTech springs that provide responsive support. They give the mattress its firm, supportive base.
Layer details from dreams.co.uk product page, November 2026.
Key benefits
- Distance from a restless partner: With 90cm each, you get 15cm more personal width than in the UK king, which means a fidgety partner's movements stay further from your side of the bed.
- Room for a small visitor: When a child wanders in after a bad dream, the 6ft width lets them settle in the middle without either adult being pushed right to the edge.
- Usable edges across the full width: Sealy's EdgeGuard edge-to-edge support means the outer strips of this wide mattress stay usable, so the 180cm is width you can sleep on.
- A steady base for a busy bed: The firm rating and twice-tempered PostureTech springs give a supportive base, which suits a bed that regularly holds a large dog or a child as well as two adults.
- In proportion in a large room: In a generous master bedroom or a high-ceilinged period room, a UK super king fills the space properly where a UK king can look a little lost.
This size suits you if...
You share with a partner who moves a lot and want real distance between you, your children or a large dog join you overnight as a matter of routine, and your bedroom comfortably clears our suggested minimum of 3m x 2.9m.
Consider another size if...
Your bedroom falls short of 3m x 2.9m, or your stairs have a tight landing turn. We'd recommend the UK king instead, for which we suggest at least 2.7m x 2.9m.
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FAQ's
What size room do I need for the Sealy Alderney in a UK super king?
We suggest a room of at least 3m x 2.9m, with around 3.5m x 3.2m feeling comfortable once you add bedside tables and space to walk round. In a loft conversion, the sloping ceiling usually decides which wall the bed goes against, so check you can sit up and get in and out on both sides.
Is the UK super king Alderney much bigger than the UK king?
It's 30cm wider than the UK king and exactly the same length, so the difference is all in width. Shared between two, that gives you 15cm more each: 90cm rather than 75cm. If your partner is restless, that extra width is where you'll feel the change.
Is a UK super king Alderney big enough for two adults and a child?
It won't feel roomy with three of you, but it gives the best chance of everyone getting a fair share when a child climbs in at night. The adults start with 90cm each, and Sealy's EdgeGuard edge-to-edge support helps the outer edges stay usable if you get nudged across.
What bedding fits a Sealy Alderney UK super king mattress?
You'll need super king fitted sheets for the 180 x 200cm mattress and a 260 x 220cm duvet. Bedding in this size usually costs a little more than king sets, so budget for new sheets and a duvet if you're moving up from a smaller bed.
How do I get a 6ft Sealy Alderney mattress upstairs?
At 6ft x 6ft 6in, a UK super king is the size most likely to stall on a tight landing turn or catch on a bedroom door that swings inward. Measure the narrowest point of the stairs, the landing and the doorway first, then compare the retailers listed on this page.