Combo feeding at 7 weeks

Hi all! I’m new to combo feeding. My LO is 7 weeks. My supply is good for the first 2-3 feeds of the day but then it slows down by mid day and he FREAKS out at the boob. So he’s not pulling out a lot of milk so I started pumping. So I pump about 2-3oz. And then I will top him up with formula to make a total of 5oz for that feeding. So if I pumped 2 oz. Then I’ll give him 3oz of formula.

Does that sound about right? I’m new to this and don’t know how to know when to start going to 6oz. Or say 7 or 8oz??