If your little boy takes the bottle with no issues then he probably doesn’t mind the flavour but you could always speak to a dietitian to see what they recommend, I’m pretty sure you can’t freeze formula though so might be worth checking that x
I use oat milk in any food I’m doing for my little girl, started off using it in the recipes for purées where it said ‘normal/breast milk’ and she now has it with cereal, porridge etc or if it’s an ingredient for a sauce, mash etc. They are fine to have an alternative milk in any food as they would be with whole cows milk, they just can’t have it as a drink until after 12 months. The only thing we were specifically advised by the dietician was to use one that was roughly 60 calories per 100ml as this roughly equates to the calories of whole cows milk as well as the iodine content. Typically this is the branded milks or the barista styles but some supermarket ones are also fine, you don’t need to buy the ‘growing up/toddler’ milks x
I've seen ppl use oat milk? It's only a small quantity used anyways.