I'm biased because I am an alpaca breeder, but alpaca fiber is one of the softest out there. It is hypoallergenic, has very little to no guard hair (so it is never itchy) and it comes in about 20 different natural shades.

I don't have any yarn on hand, otherwise I'd send some to you, but you can get alpaca at your local yarn store. It may be more expensive than other yarns, but viva la difference... it really is worth it.

I don't have personal experience with losing hair to chemo, but I have a very close friend who has, and who loves her alpaca hat and scarf.