Help/advice

Hello, my 9 month old has been exclusively breastfed since birth. However my supply can no longer keep up with him and he’s stalled at gaining weight. He is eating solids and has been doing well with that but he still likes to nurse. I know I need to supplement with formula however I’ve tried several brands and he WILL NOT take any of it. My pediatrician suggested trying it in a sippy cup which I have and he still won’t take it. I’ve also tried having my husband or someone else give him the formula and he still refuses it. He plays with the bottle/sippy cup but won’t drink it. I don’t know what else to do and I’m getting so anxious about it. This happened with my second child as well and my pediatrician and I have come to realization that if I have another baby I will need to supplement with formula from the beginning because for some reason I never make enough. It’s very discouraging and I’m trying my best not to beat myself up even though I feel a little like I’m failing him. But either way advice would be so helpful. Are there brands that are way closer to breast milk? Or methods that I can do to get him to eat it? He has another weight check in a month and I’m so nervous. Thanks for the help in advance!