Supplementing with formula

Amy
Hey ladies! My LO is 1 month tomorrow, I am currently breastfeeding and giving him 2oz of formula 8 times throughout the month. I pump and feed constantly. He never once had turned down my breasts. They say he is getting enough but he must be cluster feeding because he is never full, ever!! I feel like a wimp but it's just draining to me and I want to give him a bottle of formula at night before bed in hopes of sleeping longer and feeling Fuller. If I'm only giving him one bottle a day how much do I put in that bottle? He is almost 8 lbs. I may need to ask the Dr but I figured I could get some insight here. Thanks!!