Shimano winter boots bought a size bigger with an extra pair of thin insoles below the shimano ones. I can wear any thickness of merino sock in there with no restriction and it’s the best combo I’ve had in 20 odd year.
I stood around for half an hour in snow a few years back (with it being -10c) and still managed to continue a ride after stopping to take pics. In the 90’s I rode with Axo missions a size too small with summer socks through the winter and I remember taking them off mid ride,and walking about next to icy puddles to get the circulation going! My toes were all marked with compression and black,red,blue..