19 month old fell off crib

Last night I put my son to sleep awake because we recently had a change in day routine and he’s at preschool for a bit longer than usual so he’s been taking longer to fall asleep on me like usual. So I have been putting him in the crib if he’s taking too long and he usually cries for 5 minutes and then goes straight to sleep. But last night as I left, he didn’t cry. I thought “great we’re done crying” and 3 minutes later I hear him screaming like when he hits himself hard and I run in and he’s standing crying in the middle of the carpet. I have a carper in the center of his room but it’s not glued to the floor or anything. It’s a town street carpet that’s meant to be able to be played with using cars but it’s also not terribly padded. I checked him and he had no cuts or bruises and I squeezed and pulled on everything to see if he hurt himself and nothing either. I can’t transition him to a bed yet because we’re in the process of moving and taking things out to throw away or keep and I fear he’ll get into his drawers or closet and hurt himself even worse. I need a solution to hold for the rest of August until we move and I can transition to a permanent solution. The mattress is at it’s lowest setting and my son is also sadly very tall and chunky