My son was exactly like yours and was perfectly happy in his crib until he was three! He never tried to climb out, never once complained about being in his crib. We finally decided on his third birthday that it was time to make him feel more like a big boy. It was also our "ploy" to help push him toward being potty trained - you know, since big boys who sleep in big boy beds use the potty. :)
On his third birthday, we turned his convertible bed into a toddler bed (no rails) and just two weeks ago, we turned it into a full size bed. He's been sleeping great, save for a few nights after each change when he would wake up in the middle of the night confused.
It's completely up to you and when you feel it is the right time to make the change. I think my son would have been happy sleeping in his crib forever, but we knew it was time to make the change. If you are skipping the toddler bed, I would recommend putting the new mattress on the floor so he can get used to sleeping without any barriers. Also if he does fall out, it's not too far to the floor. I also agree with Rachel - if he's abnormally waking in the middle of the night crying, I would rule out an ear infection. Otherwise, if you are ready to make the jump into your little guy having bed freedom, do it! Good luck! :)