After spending some time in a wheel chair while recovering from leg surgery, I found that a lap robe is great but you still get cold from the back of your legs. I now make fleece robes for those times when patients have to go out in the colder weather. (Doctor appts, shopping, etc) Its just a square of fleece that is made similar to a skirt without a waist band and a full length open end zipper. The robe is placed in the chair with the zipper unzipped and then after the patient is transferred into the chair(sitting on the upper part) the robe is closed and zipped up the front. No more draft from the back. Size of the robe depends on the size of the person.
I also like the idea of the snuggy foot idea from Gail-r in Utah.