For many years my wife and I used an electric mattress warmer (Mattress Warmer), which traps the heat under the blankets. We normally keep our house temperature at 600F at night and found the mattress warmer a good way to warm up the bed before we would get in for the night. We would then lower the setting on the mattress warmer to the lowest level and was quite comfortable.

The mattress warmer died a few years ago and we decided not to replace it and just suck it up for a few minutes when we first get into bed which is a little cold. We now use a synthetic comforter, which works really well once our body heat warms up the bed.

Pete