Key things to think about when you are buying are support,
comfort and size.  Most beds are available in firm, medium and
soft ratings but these labels can vary from brand to brand. 
Comfort is very subjective.  There are no universal standards
of firmness in common usage in the UK.    Because of
this we don't give our beds a firmness rating like some
manufacturers. Your main aim is to achieve good "posture" in
bed.  Too soft and your body will slouch - often leading to
back pain - and too firm and you will cause discomfort at pressure
points such as your hips and shoulder.  Ideally the mattress
should mould to the shape of your body while remaining
supportive.  When you lie on your side your spine should be
horizontal and you should be able to turn easily. 

The heavier a person, the firmer the mattress has to be to
provide adequate support. A person who sleeps on their stomach
needs a firmer mattress than a person who is a side-sleeper. When
sleeping on one's side, the mattress must be soft enough to allow
the shoulders and hips to sink in enough to avoid pressure

A top tip to check for correct support is whilst lying on your
back; slide the flat of your hand into the hollow of your
back.  If your hand slides too easily or you notice a gap then
the bed is too firm.  If it is really difficult to slide your
hand in, then the bed is too soft and you are sinking into the
mattress, which could lead to more back pain.  If it's a snug
fit - you have the right level of support.

The mattress is the heart of your bed and the part of the
purchase you should spend most time and money on. The secret of
having a good night's sleep is the mattress and bed base you
choose. Always remember that a 'bed' is a mattress and a base
working together, you should not consider them in isolation and
should ideally always try them together.  We always recommend
you buy them together because the two are designed and manufactured
to complement one another in terms of support.  Your mattress
may show visible signs of wear and tear but the base will have had
equal pressure and strain - it just doesn't show quite so
clearly.  Another point to watch is making sure the dimensions
of any base and mattress separately sourced are compatible; two
kings might not be quite the same size!

Putting a new mattress on a base for which it was not intended
or putting a new mattress on an old base can impede comfort and
reduce the useful life of the mattress.

When assessing what you would like and what you can afford, go
for the best value rather than the lowest price. The better the
construction of the bed, the longer it will last and offer you
support for a comfortable night's sleep. If you think that every
£100 extra you spend only equates to less than 3p extra per night
over the average ten year lifespan of a bed, a bed should offer the
best comfort and support for you that you can afford.

Whilst the above information does not tell you exactly which
mattress to go out and buy (again, because comfort is personal to
you) we hope it will help make choosing your next mattress more