My preemie baby only drinks from Avent bottles

I gave birth earlier than my due date due to pregnancy complications and our baby stayed in the NICU in and incubator for a week. He only feeds from an Avent bottle maybe because the nipple is soft and is closer to a real one compared to the others that I bought. 8 months later, he still drinks milk from Avent bottles that’s why I bought the bigger ones as he now drinks 6-7 ounces per feeding.