Help!

My babies doctor tells me that I need to go up a nipple size when giving a bottle (using dr browns) says my baby is working too hard… then my lactation counselor tells me not to go up size, says that the nipple size he is on now makes him work the same as when he is breast feeding (he is mainly breastfed but give him a bottle or two a day to give myself a break). My baby is 7 1/2 weeks old