1. Boxspring
A good foundation, like the foundation of a home, is stable and durable. The foundation provides a lot of the firmness to the mattress. The mattress and boxspring are designed to work as a pair; therefore, you should try to buy them as a set if your budget allows.

2. Innerspring Unit
It is not the number of coils that a mattress has that is important - it's the construction of the coils. Most importantly, be sure that the coils have been tempered.

3. Edge Support
Edge support is an important feature in a mattress as it allows you to use the entire sleeping surface. Good edge support allows you to sit on the edge of the mattress without having it smush down like a pancake and not let you roll off the edge of the bed.

4. Upholstery
There are many different recipes of upholstery materials that can be used in a good mattress. The upholstery layers create the plusher or firmer feels of mattresses. There are many different qualities of foams - some will last longer than others. Be sure you buy a mattress that is made with high quality foams to ensure durability and comfort for years.