"Winter presents an interesting apparel challenge for those who want to play outside. Wear too many layers and you’ll sweat; wear too little and you’ll freeze your fanny. Lately, technology has offered up a solution: a paraffin-wax-like substance known as phase change material encapsulated in microscopic balls of heat-resistant plastic similar to that used in dishwasher-safe dinnerware. Coated onto fabrics, the phase change material melts and freezes before you do and, in the process, stores and expels heat energy. Clothing can now be engineered to respond to your body temperature—and heat up or cool down to keep you feeling just right.

Phase change materials work because they are designed to maintain the midpoint of a narrow temperature range. One phase change material used in fleece jackets, for example, stays between about 27 °C and 38 °C when worn—or around 32 °C, which feels comfortable next to the skin. The specific range is determined by the lengths of the hydrocarbon molecules that make up the material; in different proportions they specify different ranges."

The idea I'm suggesting here is really just an extended application - put these phase change materials in a blanket that's designed to keep you comfortable when you've got a fever. The way it is now, you toss the blanket off when it gets too hot and then have to hunt around for it later on when you start getting chills. If the temperature of the blanket went up and down to match your needs you wouldn't have to keep constantly waking up to adjust it.