If you like getting into a warm and DRY bed but don't want to sleep on electricity put a timer on the mattress warmer. Set it to come on two or three hours before bedtime and shut off at bedtime. You get into a bed that's warm and dry.
And the heat as others say will have time to move up to the top of the foam toppers. Remember that heat rises.
Heather & Jim
2017 Ford F150 4x4 EcoBoost
2013 Rockwood 2703WS