Dcold O Not Have Diabetes. When I Lie Down On

dcold o not have diabetes. When I lie down on the bed to read at night my heels get sort of numb and my feet get cold. I put the heating blanket on and other cover and they still feel cold. If I put on socks it helps a lot but tend to kick them off later. Do I have poor circulation. I have had both my knees replaced 10 years ago-would this cause it. Sometimes I pump my knees up and down and this helps. I hate to have cold feet. What to do? I am 78 years old and in good health . Thanks.