I used to sprain my ankles pretty often when I was young, so I have some experience with this. First, I assume you've done the initial elevating and using ice to reduce swelling. To sleep, you want to wrap the ankle with an ace bandage and not too tightly. Elevate your foot with a couple of pillows, if you have to get under the covers, you can make a little tent with a medium cardboard box (this may sound strange, but it has psychological benefits). I always slept best on the couch when I was injured. Good Luck!