Cold sleepers: What are your go-to sleeping socks?

I use heavyweight merino socks, usually Filson, down to about 10 F. Below that it's GooseFeet down socks.

I use thick wool socks that have never seen boots but I think fleece sox would be even warmer.

Feathered Friend down booties here. The shells come off and turn them into down socks for sleeping. Love them.

Alpaca wool socks.