I just bought a Temperpedic mattress after many years of a regular mattress with a heated mattress pad.
The salesman said I can't use the heated mattress pad because the mattress responds to the heat of the body to form itself but he said he has talked to people who use heated blankets.
I did buy a heated blanket and used it twice. I found no difference in the body molding of the mattress but I couldn't stand the heavy feel of the wires in the blanket and brought it back to the store.
I made a few of those rice bags and use one for my feet just to get them warm when i get into bed and find this works good enough to warm my feet. By the time the feet are warm the rest of the body warms up with the blankets on and I get a great night sleep.
My mattress does keep me warm I used to wake up cold, now I wake up and have to take off the quilt because once I warm up I am too hot.