Wow! four hours! That IS a lot of crying. Hmmmmm well with Wi/Wo, it is SUCH a change, I take it he doesnt breastfeed to sleep?
First of and this is just what I would do, I would try taking a blow up matress into his room and falling asleep with him in there, he would be in his cot, but u are right next to him. I would stay until he falls asleep, gently reassuring when he cries, you wont be leaving him you will be supporting him. Next night move away a tiny bit and so on and on until you are in the doorway, and then just out of the doorway. This is where I would try WI/WO, as he will have mastered (we hope) the art of falling asleep not on top of you, but on his own. Do remember this is going to require a great deal of commitment and there is gonna be a lot of crying AT FIRST. But in the end it will work I am pretty sure of it.
He will cry because he has always slept on you and will be like "hey what the hell is going on, I dont sleep like this". Does that make sense?
But, if you do feel that you would rather have him sleep in with you, rather than have the crying then I would do what your heart said, if you want your bed back and truly do, its going to be a bit of hard work but you will get there.
Also what time does he have his nap normally? wake up time? Sleep time at night? just wondered if it is kind of the same each day? my dd is 17 months and we do
Wake 7am
Nap 12 -2
Sleep 7pm