I’ve never heard of a 6-12 month formula. Do you mind sharing what it is? Also he should be ok if he is acting ok just buy another formula if you can.
I think the formula should be fine, maybe talk to his doctor just in case. As far as sleeping have you tried swaddling? White noise? Maybe a rocker if you can. If he feels full after the 5 oz, he’s probably pacifying for comfort so not really eating even though he still will get some milk while he’s there. When he starts to fall asleep, remove your nipple and rock him completely to sleep. My girl is 10 months and I’ve been slowly trying to get her off the boob when sleeping
Try using a dummy instead
We’re a human pacifier
Breastfeeding is about much more than milk, it is comfort, reassurance, pain relief, bonding.. the release of oxytocin that you both get when breastfeeding is the reason it’s biologically normal for babies to breastfeed to sleep. Dummies were invented to replace the breast. Using you as a dummy/comforter is NORMAL! Your baby is 5 weeks old it is normal to fall asleep when breastfeeding and for you to cuddle him and hold him. He’s a NEWBORN.
He might be using you as a comforter rather than actually drinking. And even if he is drinking whilst sleeping they say baby can't overfeed during BF. My little one always uses me as a dummy to sleep he only actually drinks for a couple of mins and then he will just suckle for a few mins until he falls asleep. Also I know some.babies are just hungry babies. Maybe keep a record of how much his drinking from formula and see speak to Midwife.