My son is BF and formula. However my milk stash is almost gone so he will only be formula fed & the reason why I can afford formula is through the WIC program. But I don’t really like the formula that is covers, it’s only the basic enfamil cans. I’d like to buy something a little more advanced, like the enfamil neuropro or something. But I could only afford so much on my own. So can I buy separate formula myself then when it runs out use the other cans? Or would this upset his somtach? He’s 7 weeks old