How to switch formulas

Hi FTM here, baby is officially 1 month old today and I would like to switch his formula over. We have been using Similac 360 total care 2oz pre-made bottles since day 1 in the hospital. I noticed currently it has been upsetting his stomach and causing constipation. I’m basically giving him mylicon 2-3 times a day at the moment. I would like to switch him to the Enfamil neuropro gentlease. His pediatrician mentioned we could just make a 2oz bottle of that and mix it with the pre-made bottles to make 4oz, but it seems like a lot of formula for little guy. Any suggestions or even advice for anybody else that went through this?