Dachstein mittens, which are very much favoured by climbers, are felted wool. They are brill, tough and warm when wet.
To felt to size, you need to control the process, so don't just chuck them in the washer. I would put them in hot soapy water in the sink, swish around with a wooden spoon or something, taking them out regularly and check for size.
Then when they're right, you might need to stuff them with paper (or wear them
), so that they dry right.
I think they could be very good