Nightime sleep

My little is 9 weeks old, he will always do his first stretch of sleep in his next to me, on average this is 2.5hours. After that when he wakes i’ll feed etc, wait til he’s fully asleep and pop him back but he always knows🤣 within 20 mins he’s wide awake again, if I try to persevere this lasts the whole night back and forth so I give in and co sleep the rest of the night as I actually get a decent amount of sleep then! I’ve been holding out hoping that when his first stretch of sleep gets longer then it means he’ll be in there all/most of the night. Do I keep waiting? Should I do something else? I enjoy co sleeping but when he’s allowed in his own room I don’t want it to impact his ability to sleep then🙈 any advice greatly appreciated! Things we already do; White noise Wearing his sheet so it smells like me Waiting 20 mins after he falls asleep to put him back