Definitely finer better quality wool on the inside, to avoid irritation next to the porcelain. Perhaps a lace pattern, with ergonomicaaly placed holes? then a nice thick top layer, arran or chunky. How about fisherman's rib?
Just thought - we are forgetting about the top! Doesn't a third of our heat loss take place from our heads? It needs a hat, detachable of course or we would not be able to drink from the mug without losing all that heat, that would begate the whole concept. Better have it joined to the rest at some point though, or they will get separated in the kitchen drawer (where everything goes missing)