I have found that ever since I started wearing lightweight polyester socks and uninsulated or low insulated boots, that my feet stay warmer than they ever have. The biggest issue for me was that my feet were constantly sweating. Once your feet get wet, you aren't gonna keep them warm unless you are moving. For me, keeping my feet warm falls back on the old saying, "Less is more."
Also, when I am treesrand hunting, I have found that if I'm standing a good bit, my feel will get chilly. When I am seated, I try to stretch mg feet out so that the pressure is off the bottom of my boots, allowing air to circulate around my entire foot. Wearing rubber boots that slip on versus leather boots that lace up allows for a little more room for air to circulate, and IMO keep your feet warmer in the process.