Nipple Size


So we've been having trouble finding a good nipple size/flow for our LO. I have Tommee Tippee bottles and originally had size 1 flow, those were a little too fast and my LO ends up slurping on them and getting gas trapped in his belly. So I went a size down (to 0) keeping the same bottles. Now that seems too slow because he's taking 45 minutes to finish a bottle and falls asleep sometimes in the middle of it.

I then decides to try Avent Anticolic size 2 (I had these two kinds from my shower). He guzzled down his formula and is choking on it because the flow is so fast. Also, it didn't prevent any gas from getting in his belly 🙄

Is he having trouble because I keep switching or am I missing something here? Why is 0 too slow and 1 too fast? What do you ladies use? I guess I should mention my LO is 7 weeks....