I know this sounds overly simplistic, but working muscles need more blood supply than idle muscles.  When you consider that many people with “cold feet” are sedentary and wearing stiff shoes, it makes sense that their feet are cold!  If your feet are not working, they won’t require much blood.  Feet will not work while sitting.  Feet will not work as hard to stabilize while walking in stiff and overly supportive shoes.  I have learned that by increasing foot fitness, you also improve the blood supply and circulatory system to your feet.  The more blood, the warmer the extremity.  The more work, the more blood is delivered.  So, if you want warmer feet—use them!  It’s that simple.