we just did this a couple of weeks ago. Daniel will be 2 in february but the real reason we did it is because we have twins on the way due in April and we need the crib! I worried a lot before I did it because he was such a good sleeper, both for naps and for bed. I hated to mess up a good routine. However, I figured it was better to do it now while he was in a good routine, because it most likely would be harder if he wasn't.
We skipped the toddler bed thing. Neither of my sisters did it, either. Just seemed like more work...transition to toddler bed, still need to transition to regular bed sooner or later. Of course, we also never did the bassinet thing.
When Daniel went into his big boy bed, he went straight to a twin mattress. We only did the mattress on the floor, eventually will add the boxspring and frame. What worked for us was to put the mattress in there while his crib was still there, and let him get used to it. We would lay on it with him at points during the day and talk up his big boy bed. That was a monday, we decided to start him on it on friday. For us we had to take the crib down before he slept on it. Some people I know have left it up, but that would not have worked for my son, or for us, really. So friday we took the crib down after his nap, moved his mattress to the same place (he helped daddy do all of this). He loved to lay on his mattress, but by bedtime you could tell he didn't want to sleep in it. We tried laying with him, etc, for a bit, but finally I'll be honest we just put him down and closed the door (ever since he was a baby he has preferred his door closed...just sleeps better...this also helps contain him now). I felt heartless, and I cried because he cried for 20 minutes. Then stopped. Greg checked on him an hour later and he had fallen asleep behind the door. cruel parents! He moved him to his bed and he slept all night.
The next day he cried for 5 minutes, but stayed in his bed. After that, no crying for naps or bedtime, just crawls right into bed happy as a clam. I think he just needed to adjust. He loves that mommy or daddy can crawl in with him in the morning or after nap and snuggle for a bit before getting up. We also put a basket of books and stuffed animals next to his bed, so he can play a bit if he wants.
This is what worked for us. If your son is doing well and his height is such that the crib is still fine, I wouldn't worry about it. Do what works for your family.
edited to add that Daniel is a nutcase sleeping, too. He's all over the place, used to bang into the rails, etc. But the twin mattress is bigger so he has more room to move. He have it up against a wall at the side and the head, and if he fell out on the other side it wouldn't be a big deal since its on the floor. So far he's stayed on the mattress.