My 17 month old has been using Nuk Training Cups with silicone nipples for quite a while now. It's actually the only cup he would take to when switching from the bottle. now he will drink water or juice from other sippies, but isnt interested in his milk unless it comes from this cup. I want to switch him to something a little more "toddlerish" rather than a sippy with a silicone nipple... He likes to bite the nipples, they are ripped to shreds and expensive to replace. I have tried a hard mouth cup, but he is not interested. Is there anything in between that you'd recommend/leak proof/spill proof/chew proof? I would love suggestions! Thanks!