I went down the rabbit hole of different types of animal wool a couple years ago because no matter what my feet always get cold on rides.
Apparently alpaca wool is 3x warmer than merino.
Other types of wool which are even warmer include bison, New Zealand possum, and the one of the warmest wools known, Qiviut -- Alaskan musk ox down. It's 8x warmer than wool and about a gajillion times more expensive -- it's harvested by picking the down off the ground after the animals molt -- fairly labor intensive. I think a pair of socks will run you upwards of $175.

I did not buy any Qiviut. I did buy an Alpaca wool/acrylic blend -- similar to what Smartwool uses -- from some outfit called Alpaca Direct which ran me about $20. More than reasonable for any kind of wool, let alone Alpaca.

I've been satisfied. My feet stay warmer, longer, than they do with merino wool. They still get cold but it takes longer, so I can go for longer rides in the winter.