Teat size for breast fed baby

Hi all, My baby is 6 weeks old and is breastfed with the exception of an odd bottle of expressed milk. We want to increase the number of bottles of expressed milk he gets, but he’s frustrated on the bottle (and on boob but that’s a different story…) he’s currently on a man size 1 teat but considering moving to a size 2 as I have a very fast letdown- does anyone have any advice? Thanks in advance!