11 week old won’t sleep without me holding him what do i do

it’s been a long few weeks, my baby started only wanting to sleep while i hold him which means i haven’t been sleeping at night. I try putting him down in his bassinet but he wakes up scream crying almost immediately, at most he’ll sleep for an hour. he’s 11 weeks old and i don’t necessarily want to bedshare yet, i think it’s too dangerous. we have a soft mattress. however two nights ago i finally got him to a deep enough sleep to put in his bassinet but woke up hours later with him next to me in bed. no idea how he got there. my fiancé says he hadn’t gotten up to grab him so i guess this means i did?

thankfully when i’ve woken up with him next to me he was on his back, with my arm over him and my legs bent in a c-shape, but still. i’m afraid to sleep now because apparently i’m bringing him into bed with me in my sleep. i know it’s bad and i feel guilty about it. i’m terrified of it happening again. my fiancé helping with night wakes isn’t an option. is there something else i can do? is there a way i can safely co-sleep with my baby that doesn’t involve me sleeping on the carpet? advice appreciated.