combi feeding teat size with comfort or reflux formula

[NickyKB]

I mostly bf but LO has 1bottle of formula a day. He's 6 weeks now and always had a lot of spit up. this has got worse recently despite my going dairy free and having pepti formula so I'm thinking of trying comfort or anti reflux instead for his bottle feed. I use avent classic bottles with size 1 teat would the other formulas be too thick for this? I don't want to end up with too fast a flow so he stops breastfeeding...

Also does comfort milk help for reflux symptoms as I'm a bit wary of the full anti reflux milk as I know several people whos babies got very constipated with it.

thanks