This afternoon, I pulled his crib mattress out of his crib so he could romp and play on it. So at naptime, I decided to try and get him to sleep on his mattress on the floor. I put a child-proof lock on the inside door knob in one room, and a baby gate up on the door in the playroom. (He has 2 connecting rooms: a bedroom and playroom, and a door in each)
Then I went shopping! :)
Daniel said it took him about an hour and 15 minutes before he finally settled down and went to sleep, but he did sleep on his mattress for 2 hours! I guess when you've got two whole rooms with toys to play in, it takes longer than normal to settle down. But I'm very happy. He's getting big enough that I'm not sure how much longer his crib will hold him.