Another option for "thin ice" -- if a large figure steps on it, it changes to a water hex. The ice broke, in other words. For small and medium guys, just treat it as a normal hex (or normal ice hex) unless it is broken.
Of course, this requires you to have extra water tiles, and to rebuild part of the board during the game, which is kind of a pain.
Actually, I kind of like this one as well. Pretty creative.
I just thought the official rules for snow and ice weren't very imaginative. They basically play as normal hexes or sand. And we hate sand.