Hi. My son is 18 months old, and we started the gradual process of switching from milk to formula at 1 year. Here's what we did:
1. At first, we just put 1-2 ounces of whole milk in his 6-ounce bottles. He started having diarrhea, so after a few days we went back to just formula. We waited two weeks.
2. We tried again with the 1-2 ounces of milk in the bottles, and he didn't get diarrhea so we just kept this ratio for about two weeks.
3. We increased to a half milk/half formula mix and did this for about one month.
4. Then we did 2 ounces of formula and the rest milk for about two weeks.
5. Then just milk. And he's been doing only milk for about 1-2 months. He's just fine. And he seems to have a better appetite now, so that's good.
Hope that helps. Good luck!