He's not ready to be there full-time. Start him with naps in the crib. Also, putting a buckwheat pillow up against the top of his head will make him feel like someone is near...and he'll sleep longer....also, keeping him warm, like in bed is key....we got a down alternative blanket from Costco. They get colder in the crib. (I'm going to get burned at the stake here, but we also put a really soft warm blanket on the bottom, like a nest and that works well.) Bringing the crib right next to the bed, so he can hear your breathing might be helpful, as well.
All of our kids, so far have transitioned out at around 18 months easily...except kid #1. He was almost 3 and I explained that another baby was coming and it was only FAIR that the baby set equal time. He agreed and started sleeping in his own bed all night long. We did transition him at 18 months to a crib mattress on the floor next to our bed, so that when he woke up, we were still right there. My kids never slept well on a crib mattress - you know how hard they are???? We've always transtioned them into a real bed with real sheets and comforters and pillows, just like our bed.
Don't listen to anyone who has not co-slept. I don't give them advice on something I've never done, and they shouldn't give advice in an area they have no experience. It can be easy, but like with anything, it's about that individual child. My kids eat asparagus and broccoli without sauce all over it, many parents don't feel their kids anything but chicken nuggets. We are all different, as are our children.