Hi Ruby acres,
Heat can have an effect on the durability of temperature sensitive foams such as memory foam and gel memory foam so I would tend to avoid these with a heated mattress pad (or at the very least I would use it very cautiously … see post #2 here).
It will have much less effect on materials that aren’t temperature sensitive so they would be fine.
The first place to start is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choice … and know how and why to avoid the worst ones.
Phoenix