Way back I had a water bed. We lived in a house with no central heat or insulation. The water kept me very cool during the summer, but quite similarly winter time it could also suck out all your body heat. What worked well was a wool blanket between the bed and an electric blanket. I still keep a few wool blankets, I don't know if there's anything warmer. If its cold enough to throw one on top of the bed I usually need to remove it in the night. Because of its fire resistance, if its not on my bed its nearby in a drawer with the emergency fire escape ladder.

The mattress pad makes our cold bedroom comfortable.

http://ecorenovator.org/forum/attach...-bdrm_temp-jpg