The mattresses from Serta and Simmons are basically the same.  Mattresses have the same basic components and there are certain things you should look for depending on your comfort level.

A mattress is made up of several important features:

Coils
The inside is the most important part of a mattress when it comes to supporting the body.  The core of a mattress is made up of coils.  The number of coils should correspond with how much support a mattress gives.  That is, a mattress with 300 coils will provide less support than a mattress with 700 coils.  Generally speaking, the more support you want...