I try and use as much natural fibers as possible. I've been sold on the wonders of wool since my kids were little and their Waldorf teachers showed me how warm and waterproof wool mittens and socks can be.
I made myself a wool sweater for those chilly New England Fall days and found that I could layer with a wool sweater way into the winter.
I probably would prefer a blend or a lighter weight wool for something I was going to wear inside.
I like Plymouth Encore cause it's mostly wool and not too expensive and there is a great selection of colors. I'd suggest it for a first sweater project.