I buy a lot of wool sweaters for my projects and not all of them felt as nicely as I want. The sweaters are already cut up before I wash them so there is no wearing them or re thrifting them.
SEW!!! I decided to try covering buttons with the not quite felted wool. I ordered my button blanks from Atlanta Thread & Supply Company. They are open to the public. They sell in bulk with no real packaging (also great place for zippers) with excellent prices. The buttons come with two parts: a front domes cap and a flat back with the letters PRYM. You don't need any additional tools, other than scissors (if you don't have e die cutter with a circle die).
Center the metal top on the fabric.
Gently push the fabric onto the prongs inside the button cap. Push in one side then the opposite side, all around evenly. There are more images up at flickr.
Carefully snap the backing piece onto the front cap. Once this is done it is very hard to get undone so make sure all of your fabric is neatly pushed into the cap.
Hairband with wool covered button.