If u can afford it, and your son enjoys it, what’s to stop you from continuing with formula milk? U can also intro your son to fresh milk, UHT milk, soy milk, etc and see what he likes. Their taste buds will keep changing so it doesn’t mean now dun like, then that’s it, or vice verse. I gave my gals formula, but also intro them to other types ard age 4 and slowly, we began to make the transition out of formula milk. So from like 3 feeds of formula, it dropped to 2, then 1, then finally, no more.
personal preference, some switch to Fresh Milk. I will continue for my both kids till they say don't want and switch to Fresh Milk.