I agree that you should start the toddler bed asap if he is a jumper. My son is almost 22 months. A couple weeks ago, I went into his room to get him out of his crib in the morning and he was leaning over the side of the crib. Well, before I knew it, he leaned over the side and flipped right out. For the grace of God, I HAPPENED to be right there when it happened and was able to catch him before he hit the floor. It scared the living daylights out of me though. I just hate to think how much he could have hurt himself had I not been there to catch him. I had no warning that he could do this either. He had never attempted climbing out of his crib or anything like that. It just came out of the blue. So, my advice is that if you think there's any chance whatsoever that your son might be able to fall out of the crib, that you should switch to a toddler bed immediately and not take the chance.
After the incident with my son, I refused to ever put him back in the crib again. We actually put him to sleep in his pack and play for two weeks until we were able to get a toddler bed. That worked well for us because it was lower to the ground than the crib, and the sides were taller so it was much more unlikely for him to be able to get out. Even so, we still put tons of pillows on the floor surrounding it just to be safe.
We finally got him a toddler bed this past weekend, and he was SO excited to go to bed in it. The first night, he didn't even want to be read any bedtime stories (which he normally wants to read tons of books.) He just wanted to skip all that so he could get in his "big boy bed." And we've had no problems at bedtime. It's just been great.
I will say though that as well as night times have gone in the bed, nap times are a different story. He just thinks nap time is now play time and we've yet to get him to go down on his own in his bed for a nap. So today, I pulled the pack and play back out and put him down for a nap in there. My plan for now is to do the pack and play for nap time and the bed for night time and we'll slowly transition to the bed for naps when he's ready.
Just make sure that when you switch to a toddler bed to make sure his room is baby proofed. We put a gate in my son's doorway so that he can't get up in the middle of the night and wander around the house. We also made sure his room was well baby-proofed.
Good luck to you!