Our oldest was 18 months old when we moved his crib mattress that he never slept in, to the floor next to our bed. He usually ended up in our bed, which was fine. Then, he moved to a twin bed in his own room, and he ended up in our bed every night. At 3.5 years old, we told him that he needed to start sleeping in his own bed since his brother or sister was coming and they needed time with us without anyone else. He was all about things being "fair" at the time, so we said, "It's only fair to the baby, since you've had 3.5 years with us, without sharing." He replied ok, and that was it. (He weaned himself at 16 months.)
Our 2nd son was 16 months (he had just weaned himself, as well) when we started moving him to a crib in his brother's room. He slept better by himself, since he moved ALL night long. He also slept better hearing our older son's breathing at night.
Our daughter was moved her bed at 18 months. She was exclusively breastfed for 18 months and refused to eat any solids or take my milk in a bottle - she'd go 8 hours and not eat a thing, if I was gone. Finally at 18 months, I left for 4 days and she started eating 4 hours into it. She also started sleeping through the night, so , we moved her into her own room. She sometimes wakes up and calls for us, so I'll go and get her and she spends the rest of the night in our bed.
Of course, now that he's almost 8 and our others are 4 and 2, we sometimes get visitors in the middle of the night, but our kids sleep in complete silence and complete darkness. They have no fears of night time scaries. Our boys have a double queen bunk bed, but they usually sleep with each other on the bottom. Our daughter is 2 and she has no problem sleeping alone, but sometimes she needs mom and I'm ok with that.
Our kids are confident and talk to adults as well as they talk to kids. In fact, I own a business in a small shopping center and my 2 boys go to the store together, order sandwiches at the deli, wait for them, pay for them and return to my office.
Every child is different, so you are going to have to appeal to his needs/wants when transitioning him.
I can't imagine forcing my kids to scream when they are scared or need reassurance. Good for you for co-sleeping. I think every parent needs to raise their own kids the way they feel is right....for that individual child.