Just remember, when you start layering these mats, to make sure they are still firm enough to support your ankle. You don't want them so squishy that your ankle wobbles.
I just recently bought some at Lowe's and am anxious to see how they work. I haven't tried them yet though. And mine are black, 2x2 feet each, and come in a 4-pack. I think they're about 3/8 inch thick.