Ahh, i need advice about weening and formula...

Erbear
Hi! So my son had weight gain issues his first four months, because of that I was advised to start solids and supplement with formula, offering a few ounces after some of our nursing sessions. As a first time mom, I freaked out when he wasn't gaining weight, didn't trust my body and did what I was told. I had always heard babies will refuse when they aren't hungry, and he never refuses anything, so of course I felt guilty and offered him more formula and more food. Well now I'm afraid that my breast milk supply had tanked. I find him eating more and more solids, and know that breastmilk or formula should be his main source of food at this point (he'll be 7 months on Jan 23). So now I feel like I need to just switch to formula, which is tough for me, because I'm not ready to be done breastfeeding, but I want to do what's best for him, which I think breastfeeding is, but he's clearly not getting enough, and trying to guess how much he's getting from me, then offer the right amount of formula etc is just too much of a guessing game. Do, question is, how much formula do I offer this dude? 6 oz every four hours? Plus food? I know a lot of people don't even make it this long breastfeeding but I can't help but feel guilty, ah mom life! Also, how does weening go, should I be pumping a few times a day to relieve any engorgement? I just want to get us both to a place where I know how much he's eating so I don't worry that he isn't getting enough. Thanks!