What’s the next step after formula?

My son recently turned one and is now on whole milk. He does eat solids and I try to give him as much foods with vitamins and things he’s needs but he’s such a picky eater and doesn’t really eat a lot yet so I’m still worried about him getting the vitamins he needs.

I read after formula if you don’t want to give whole milk there’s something else, I think I seen one for toddlers in formula also and one in boxed/canned drinks. Can someone help me or tell me what’s best? Because since he doesn’t eat a lot a day he still likes his bottle every 4-6 hours & im not so sure how that’s going to work when we go out because he doesn’t just take water.