The way I understand it, the pain we as CRPS/RSD sufferers feel is connected to the sympathetic nervous system. As that part of us starts to feel pain, our body's natural response is to limit the blood flow to that area which results in lower temperature.

I do not have any tips to keep your foot warm and still be able to function. The only time I am able to get out of the house is to go to a doctor's appointment. I am unable to wear anything on my foot, so it does get very cold, especially when we have days like today when it is all of 16*F last I checked. When I am at home, I usually keep my foot next to a radiant heater to keep it as warm as possible. We keep the door shut in that room to keep that room warmer than the rest of the house since my husband does not like the warmth as much as I do. Like many others here, my bed is tented off to keep the covers from touching my foot. My husband made a foot board for my bed that the covers drape over and seal in my body heat. Unfortunately we sleep in two separate beds right now since my husband was worried about accidentally hitting my foot in his sleep so much that he was not sleeping at all. The air space eventually warms up and keeps my foot warm. I do like Catra's idea if you are able to put a sock and/or shoe on. I used to work outside and those foot and hand warmers were a lifesaver in the winter.