I don't let my DD cry it out. She does not co-sleep with us, but she did sleep in our bedroom in her pack and play until she got too big for it. She is currently 7 months old and sleeps fine in her crib. I think it was harder on me than her.
How I got her to sleep in her crib was a process of nuturing. Basically, if she cried as if she needed me (actual crying and not a whimper), I would go in check her diaper. Change her if she needed it. If that was all she needed, she would go back to sleep. If not, I give her a bottle and she eats until full and goes back to sleep. I put her back in her crib. If she had cried at this point, I would rock her until she went back to sleep. Always making sure her needs are met: diaper, hunger, snuggle.
The fact is, she has built up a trust that I will be there when she needs me. She does not feel abandoned in her crib. She is the happiest baby I know. She wakes up once a night (normally after 8 hours)... eats and goes back to sleep for 2 hours. She wakes up playing with the mirror in her crib for about 30 minutes and then cries out for me. I go get her, and we start our day.
Put yourself in the little guy's shoes. The person that has always been there for you is making you go cold turkey and isn't answering you when it has always worked before. I wouldn't personally like that.
Lastly, I do put her in a zip up blanket at night, the wearable kind. Since he is used to sleeping with you, he may be cold. The blanket gives them a sense of security. You can always tell if your baby is too hot or cold by testing the back of their neck.
This is just what I have done for my little one. Good luck!