I started swapping nursing sessions/bottles for dairy snacks. For example I switched one bottle for a smoothie with Greek yogurt and whole milk Then another snack I'll do cottage cheese or string/babybel cheese with fruit or crackers I haven't started offering whole milk by itself yet planning on just offering some during meals out of a straw cup or sippy cup and cutting his middle of the day bottle/nursing Then we'll just do a hard stop on the first thing in the morning nursing session and right before bed session
My son ped said at 12 months give a small amount of straight whole milk. We started with 2 oz and then the next day did 3oz and planned to continue on that path. However my son has a dairy allergy so we had to move to soy milk but we still did the same thing. He says you'll know almost immediately if a child has an allergy because they'll have blood or mucus in their poop
How I did it was I still give him formula but started putting whole milk in his sippy. And then I’ll just replace the formula completely once he’s fully use to drinking the whole milk. I didn’t do the half formula, half milk thing. And it seems to be working for me.