First it starts with good footwear. Now this can be a trade-off. The more support and stiffer the boot is the colder your feet are going to be pretty much regardless of the insulation.
That why even the best mountaineering boots people lose toes - there is plenty of insulation but the boot is too rigid and therefore restricting circulation. For mountaineering this cant be helped because you need supreme support to hold crampons on, front pointing and for those steep and rugged hills and ridges. On the other end of the spectrum is soft bottom mukluks or kamiks used by the Inuit or Athebascan people. The warmest of these designs are the ones made from smoke tanned moose hide. They are like big bedroom slippers lots of room for circulation and to wiggle chilly toes. They are also extremely light putting no added stress on legs during those long ski or snowshoe runs.
The down side is that they have no support. So hills and rugged terrain can make it difficult to get good footing an also make for sore feet at the end of the day. So it is up to you and your activity to determine how much or how little support and insulation you will need in your footwear. For extreme cold, no matter if it is a stiff boot or soft one, I layer my feet like this: Foot - from skin out: Thin wool liner socks, a vapor barrier liner (heavy duty plastic bag), a medium then a heavy weight insulated wool sock with some synthetic fibers say 25% to help speed in drying. Boot - from the inside out: a perforated mesh insole to capture snow and frost, then an insulated insole of synthetic felt with perforated reflective Mylar, then a insulated synthetic felt boot liner with reflective aluminium. Thicknesses of insoles and liners will depend on temperatures your needs.
By Lonnie Dupre