I had this same issue. I have a baby that honestly had a lot of neck control very easily. He only fell asleep on his stomach and likes his felt baby blanket to drape over his head for him to be able to fall asleep in his bassinet. He’s 22 weeks old and has been sleeping like this since three months old. I don’t advise it and the pediatrician also said that it’s not the safest but he’s a very active baby and he crawls out of the blanket every time he wakes up or pushes it off of himself and stands up the side of the crib when he’s done with his naps. You could also Try a covered basket.
My LB is the same he won't sleep without a muslin for comfort, I think it is a sensory thing as me and my partner are neurodivergent, he rubs it around and plays with it in his hands. We just supervise and remove when he is asleep. I swear he wants to give me a heart attack though 😭
Yup my little boy was n is still the same at 9 Months . Likes something on his face so he had a muslin n I just removed it when I wasn’t watching him (sleeping myself) now he was a comforter
Muslin is probably safest but I still wouldn’t risk it. It sounds like he is wanting the darkness. Also just from someone who has just gone through the painful process of removing the dummy from a 11 month old being used as a sleep aid - I’d try to not use anything for them to settle, just a good old cuddle or white noise x