First thing is a wind break of some sort. My feet rarely get cold, when it is way cold out I have two wool Army blankest sewn together in an *L* easy in easy out. My Meindl boots are good to around -15.

I've found if I keep my kidneys,neck and head warm the extremities usually take care of themselves.

I can recommend German Army Tankers coverall liners (surplus). A layer of long johns, then the Tanker liners then the insulated coveralls, good to zero. Below zero I add synthetic sweat pants and a wool sweater. The thing about the coveralls and liner is you can open the zipper to vent them. Socks are always double wool. The liners pass moisture but trap air, they rally work out well for me and they are cheap.