Help! Bedsharing to cot

First up just let me say I know how dangerous bed sharing can be and I’m not even going to try to dispute it. But I bed share with my almost 4 month old. When he came home from the hospital he slept great in his bassinet, when napping. But at night he would cry and fuss anytime I would try to put him in it. I tried white noise, shushing, swaddling, not swaddling and the dummy. Nothing seemed to work. In the first week of his life I survived off 11 hours sleep. I would stay up all night until his dad woke, I would sleep for 1.5 hours and once I even got 2 hours! I ended up falling asleep on the lounge with baby in my arms and decided it was safer to lay on the bed with him. So fast forward to now and he still sleeps in the bed with me. We try to do it as safe as possible. I use one pillow myself and no blankets at all. Being summer where I live makes that easy enough. But it’s starting to get colder and my body aches from staying in the one spot pretty much all night. I feel we would all benefit from him sleeping in his cot, which is in our room.

Tonight I tried putting him into his cot once he had fallen asleep, even if it was only for the first sleep cycle. He was barely down for 2 minutes and was screaming. He started fussing straight away and I left him hoping he would self soothe, which he does when he is in the bed (he can be left alone in the bed for naps just fine). He started to cry so I gave him his dummy. I tried everything I could think of until he started screaming. I picked him up and brought him into the bed again. How can I get him to sleep on his own?

And when he does how do I cope? I worry that something will happen to him and I won’t notice because he is not right next to me.