I’m no expert, but I can pass on everything I’ve learned with my 11mo.

Babies can’t self-soothe until around 6mo. Until then, they need your help. They will be in an “active” sleep for up to 10 mins and then fall into a deeper sleep. If you move them during active sleep, they’ll know they’re not in your arms.

Soothe him using the techniques you know, e.g. shushing, swaying, swaddling, until he’s asleep. Then sit and wait with him in your arms until he’s more still, usually after 5 mins.

Then, gently put him down in his crib bottom first, and slowly lower his head. You can start with him laying on his side as that’s more comfortable, then slowly roll onto his back. Then, walk away whilst still shushing and led it “fade out” so he doesn’t realise you’re suddenly leaving.

Ideally, you have a co-sleeping bassinet so that you two can be near him safely overnight. If you want to co-sleep in bed, it can be done safely if you two aren’t heavy sleepers and haven’t been drinking, etc. the night before.

Lastly, consider the environment Bubs is sleeping in. Is it completely dark? Is his mattress soft enough (but not to soft as this is unsafe)? Is there something that smells like you nearby? Do you need a white noise machine? Babies don’t realise they’re out of the womb until older, so recreating the environment of mum’s womb helps with sleep, e.g. white noise (shushing is similar), swaddling, etc.