Hello everyone. My son is 8 months old. He keeps asking for my breast …

Hello everyone. My son is 8 months old. He keeps asking for my breast all night, but there's not much milk. I think he's not getting enough and his weight might be two to three months behind. What kind of formula should I choose? I want to supplement feeding him. He eats porridge and puree now. He has no teeth yet. Thank you.