Firmness is the gold standard for mattresses. Traditional wisdom is "the firmer the better." This however does not mean you have to give up comfort and sleep on a board. Firmer beds provide more support for your body, but many mattresses today have "pillow tops" or other soft surfaces that combine the comfort features of soft mattresses with the support of hard beds.

The size of bed you want depends upon the room you will be putting it in and the size and number of sleepers. The smallest bed is a twin bed, while the largest, a king size bed, is as wide as two twin beds, but longer. A full or double bed is wider than a twin, and a queen size bed is even wider, and possibly longer. Since most people move at least 40 times a night while sleeping, most professional advise a queen or king size bed for couples sharing a bed. However, in small bedrooms a double bed accommodates two while leaving more floor space for walking.

When comparing mattress prices, make sure you are also comparing materials. In the past, foam rubber mattresses were cheaper than the innerspring versions, but some of today's high-tech foams can be durable, comfortable and long-lasting. Mattresses without inner springs tend to be cheaper.

Mattresses usually come in sets with box springs. The box spring is also called the foundation. An inexpensive set may be cheap because it includes an inadequate box spring. Check the box spring alone. If it seems extremely uncomfortable, it may be noticeably uncomfortable even underneath the mattress. Make sure it is well framed. If you notice there is little support except around the edges, or if the edges or narrow, this will give many places where the mattress might shift or sink.