Supplementing Moms how do you do it?

I just started supplementing with formula about a month ago because I'm dissatisfied with my sons weight gain although he is gaining the proper weight. I'm not sure if I've got it down correctly though, I try to give him as much of it as possible just in case he's been missing vital nutrients from breastmilk alone and I give him as much breastmilk as possible too. Stools have been nice and everything appears to be going well but do any of yall have any tips I could use?