I'm probably going to start combo feeding LO soon. He is currently 3 months old, EBF, and I'm back at work. He will probably start out getting an occasional formula bottle here and there when I don't pump enough, and as he gets older I may use formula when we're on vacation and I'd like a drink or when we've been out on dates night etc. So he will get a formula bottle anywhere from a couple times a week to a couple times a day.

Where I'm stumped is how much formula do you use? He currently gets 4-5oz breast milk bottles per feeding when he's not getting it straight from the source. Do I just make a 4-5oz formula bottle as a replacement? What happens as he gets older? How do you work it when their required formula volume increases but their bm volume doesn't? Am I over thinking this?

I can't find any answers online so I'm hoping there's someone who has been there and done that. Thanks!