@Riana just wanted to share this advice from my HV as she has replied and might help you :) I think just judge it on how he takes the milk, if he's fine on the No 1 teat just leave him on that, you don't have to change the teat.....
I think if you want to ensure that a baby doesn't develop bottle preference you should keep a small teat so the bottle doesn't become easier to get milk from
Following as I’m in the same situation