Desperate! Help needed for getting baby to sleep


So a bit of back story. My husband and I don't particularly like the CIO method, but we are at breaking point and somethings gotta give!

Our baby slept in a bassinet for about 4 months and a bit. He then got too big for it and we switched him to his crib. We've always put him down asleep and he stays ok. One time we just put him in the crib awake with some white noise and he eventually drifted to sleep on his own. But that has happened only once, and never again.

He then started with the sleep regression and being absolutely exhausted we gave in and had the baby sleep with us. It wasn't the first time, we had him sleep with us the entire night other times (when he'd gotten his shots, for example). And also normally after the last feed of the night we have him in bed with us for some cuddles.

Problem is, he now only sleeps if he's being held and rocked. I have to admit that I am partly to blame, as during the day he naps on me. Thing is, I have extremely important exams coming up in June and I admit it is easier to get him to sleep on me for an hour or two, because that way I can actually study!

For the past couple of nights this behaviour has crept to night time sleep as well. He'll wake up for a feed, and then won't go to sleep unless held and rocked. Before he would either drift of to sleep while nursing or shortly after without needing to be rocked. He is sleeping with us, so he is not on a room on his own, we caress him when he cries, so he knows we are there, but it makes no difference. We tried sort of CIO yesterday, as in, we didn't pick him up, just laid next to him, and try to get him to calm down/sleep. He didn't calm down, the crying escalated, he was hysterical.

Obviously this situation cannot continue. We are exhausted, and naturally our patience is running VERY thin, which I am sure only adds to the problem.

Can anyone please help?! Recommend some books? Or method? Anything please!!! Baby is a very light sleeper 5 month old. THANKS.