Sorry it's so long...please hit me with any suggestions!

My LO is 4 weeks old and just now at birth weight. He's not losing, but he's not gaining either. We are supplementing with formula for extra calories twice a day. He would sleep 6+ hours at night if I didn't wake him. I already pump the side he doesn't eat from and he falls asleep so quickly at night, I don't feel empty. Could I pump at night and offer him a bottle? I just nursed him for an hour but he slept for half of it. I switch sides when he falls asleep and got 3oz combined that I could offer him to ensure he's getting enough milk? What do you ladies think?