I hope someone who is not experienced does not read the following and presume it is good advice - it is from my personal experience and not to be followed under ANY circumstances!!!
"Back in the day", i wore "large plastic bags" (AKA bread bags
) inside my "snowmobile" or sorel-type boots (actually, Lacrosse brand equivalents b/c thats what the only store in my home town carried). They were warm enough, though the felt liners got beat up pretty bad too quickly and didn't walk up steep stuff very well. They were also heavy and "clunky". I can also remember Moon boots - kinda warm but impossible to walk up anything steeper than the stairs...
I got older, moved to more "hilly" terrain and then, viola' - double boots all the way.... Nowadays, i still use my VBL sock system (evolved from the bread-bag strategy my Canadian Gram taught me), LaSportiva Nepal Extremes, and OR Brooks Range overboots/gaiters. This combination climbs beautifully and so far, never a cold toe - (knocks on head...)
Keeping warm in the winter is remarkably simple; keep everything dry, remain well-hydrated, use "just enough" insulation to keep warm, but not too much so that you get wet (from perspiration) and if all else fails, keep moving. OF course, YMMV....
fm