Sidecarring the crib ??
When dd got mobile we taught her how to get down safely. Worked well.
I put our mattress on the floor anyway because when DS first started crawling he would crawl all over the place at night- screaming his head off, not asleep but not awake, good times, good times - due to developmental leaps he was making daily + teething, but I taught him to get off the bed backwards so he was fine on other beds and on ours once I replaced the boxsprings and frame about 6 weeks later. Just demonstrate how to climb off the bed backwards, you'll be surprised how quickly DC can pick it up. The fun part is that it makes them think they can get off anything backewards (re: dock).
This thread is old, but this question didn't get answered. Is it safer to have the crib slightly above or below the level of the bed?
Gooseberry, I padded underneath the crib mattress to make our sidecar exactly the same height as the bed. That way I can scootch in there to nurse, then easily get back to my own sleeping space. It's like one big giant awesome bed! I sleep pretty close to the crack between the beds, so that DD can't crawl out of the sidecar without crawling over (and waking) me.
If you want it different heights, I'd make it a couple of inches lower. The Arm's Reach Cosleeper is set up that way (about 3-4 inches lower than the bed mattress). It's designed to keep baby from accidentally rolling into your space and getting tangled in your covers.