For us at 12 months we were already partially on cows milk. He would have a formula / cows at bedtime and then only cows for the rest of the day in a straw cup. Just have as much ir as little as he wanted the the straw cup back in the fridge.

Now he has milk on his breakfast and sometimes a glass at dinnertime but otherwise he gets his calcium through sources of cheese and yoghurt and only drinks water during the day.