DS is sitting up and getting on all fours while on his belly. This morning he was on all fours rocking back and forth. I'm thinking it's time to drop the mattress even though he's a long way off from actually pulling himself up or being able to put himself in a sitting position yet.
Have you dropped the crib mattress yet? I love our crib but it's a PITA to drop the mattress since you basically have to take apart 75% of it.