Best bottles for gassy/irritable baby?

Jessica
My son is 4 weeks old, and he gets both breastmilk and formula (Was on Enfamil Newborn, yesterday was switched to Enfamil Gentlease). He drools a lot of the milk out, gets irritable when eating, and has gas throughout the day. We've been using Avent bottles but I think he needs a different brand. Any suggestions on what's worked for your gassy baby?