I bought these mittens years ago, and have returned to them again and again. The boiled wool is so dense and thick that they are waterproof in practice. They are extremely warm and do not become damp inside. And they are bombproof, much more durable than typical nylon/gore-tex mittens. They are also cheap.
The only downside is the bare wool can be slippery. I have seen people spread a little silicone caulk over the palm to improve the grip. Maybe spray Plasti Dip would work, too.