Baby eating too fast

My little one is a three and a half months old. Starting the past couple weeks she has been spitting up with every feeding it seems like. It's not projectile or the whole bottle, just a little. I personally think she drinks it too fast and it not being the formula. We use the playtex ventaire bottles with the slow nipple. I try only feeding her half the bottle, then give a little break ( if she lets me lol). Her pediatrician said to try different ines to see what works best.Any recommendations on different bottles?