Well, it may not upset him as much as you think! I waited with Tyler until he turned 1 and we started dropping bottles and doing whole milk. We went gradually, and he was a pretty enthusiastic solids eater, so it didn't bother him a bit. If you want to go ahead and switch now, really the only advice I have is that if it does upset him, don't waffle. Babies thrive on routine and knowing what's next, so if you change it up, it shouldn't take long for him to get the hang of the new way of doing things.