We slowly changed DS from formula to cows milk at around 14 Months....We started making up 180ml bottles of formula then topped it up with Cows milk, and slowly made smaller amounts of formula until it was all cows milk....so it was a slow thing, but he didnt notice any difference at all.
As with the sippy cups, DS still has his drinks in a bottle, as he mucks around too much with the cups....He fills his mouth with water from the cup, then lets it spill out! The non spill sippy cups, he hasnt learnt to suck properly....So we are going to try again later!!! Good luck with it all.