I'm actually going through this now. DS has been down to 2 bottles a day for a few months now... and he is down to about 400mls a day, this includes milk in his cereal. He has been having cows milk in his cereal for about a month now, and over the last 2 weeks I have been mixing formula and cows milk in each of his bottles. He doesn't seem to be having any issues with this, so it's just a matter of me taking the plunge and dropping the formula completely.