Merino socks , summer SPDs, and neoprene toe covers
Preference is Ron Hill winter tights.
Brynje mesh base layer, long sleeve
Alpha direct insulation layer 90-120g/m^2 weight
Windproof or waterproof chosen based on level of precipitation
Buffalo pile / pertex mitts
Cycling cap, supplemented by buff if really cold or sometimes beanie.
Worked just fine down to -6C of late. Coldest I’ve cycled is -11C and I suspect the above would be fine for that as well. Also fine at 10C etc.