Sealy PostureTech Alderney King Size 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
£599
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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
- More room each than a UK double: Moving up from a UK double gives each of you 7.5cm more width, which means a little more space to turn over without nudging your partner awake.
- Length for taller sleepers: At 200cm (6ft 6in), the UK king is 10cm longer than a UK double, so a tall partner's feet stay on the mattress instead of hanging over the end.
- Easier on different body clocks: If one of you gets up hours before the other, 75cm each lets the early riser slip out on their own side without clambering across.
- Edges you can sit on: Sealy's EdgeGuard edge-to-edge support keeps the sides of the 150cm width supportive, which helps if you're recovering from an injury and need a steady perch to get up.
- The same firm feel on both halves: Both sides share one firm rating, so a UK king of the Alderney suits couples who agree on firm support rather than a pair split between firm and soft.
This size suits you if...
You share the bed every night and keep drifting into each other's space on a UK double, one of you is near six foot and could use the extra length, and you both like a firm mattress with a little cushioning on top.
Consider another size if...
Your bedroom is smaller than our suggested 2.7m x 2.9m for a UK king. We'd recommend the UK double instead, which needs at least 2.6m x 2.8m.
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FAQ's
How much space does each person get on a Sealy Alderney UK king?
Two people sharing the UK king get 75cm each. That is 7.5cm more each than the UK double, which gives 67.5cm per person. It sounds modest on paper, but it is often the difference between sleeping undisturbed and feeling every turn your partner makes.
Is the Sealy Alderney UK king long enough if you're over 6ft?
The UK king is 200cm long, or 6ft 6in, which is 10cm longer than the UK double. If one of you is around six foot, that extra length is often the real reason to upgrade, more so than the width.
What room size do I need for a UK king Sealy Alderney?
We suggest at least 2.7m x 2.9m, with around 3.2m x 3.2m feeling comfortable. New build main bedrooms can feel tighter once fitted wardrobes are in, so measure the floor you actually have left before ordering.
Should we get the Alderney in a UK king or UK super king?
The UK super king is 30cm wider and the same length, giving 90cm each, so the UK king gives 15cm less each. The UK super king needs a room of at least 3m x 2.9m. If your room fits it and you want maximum separation, size up; otherwise the UK king is a sensible middle ground.
What bedding fits a Sealy Alderney king size mattress?
Standard king sheets fit the 150 x 200cm UK king, and a 230 x 220cm king duvet covers it. Double bedding will be too short and too narrow, so plan to replace your sheets if you're upgrading from a UK double.