when our house was oil heated we had one on our bed which was great! We'd turn it on a half hour before bed to warm everything. It was the nicest thing to crawl into a warm bed. It was the kind that covers your mattress and then you put your sheets over top.
My son has on on his bed as he really loves a warm bed.
They aren't the fire hazards like they used to be, so don't be afraid to use one, and they don't get hot enough to hurt you either.
We have the same thing. It's a pad that goes under the sheets.
We turn it on just before we go to bed and hit the preheat button which will preheat the sheets and blankets for you. Once I climb in bed, I turn my side off and the wife keeps her side on low (it goes from low which is 1 to High which is 10)
This one uses low voltage so it can't cause a fire and it has sensors in it that adjust the temp constantly so it never gets hot.