Yeah, wool is hard to beat for warmth, especially for hiking because wool stays warm when wet; great if your feet get wet.
Can you do angora rabbit hair by any chance? That's even warmer than wool, so much so that some say it's too hot to wear in most conditions. Works well in a blend though. You could try a cotton blend, like Serenade
, or a Debbie Bliss cotton/angora which I think is now discontinued, but apparently some can still be found
. There's also this synthetic blend
, and this 100% angora
which is on close-out.
Sorry if you can't do angora. I don't know, among non-animal fibers which, if any, might be warm enough for your purpose. .... I hope you can find something that works for you! Let us know if you have success!