I would agree that an air mattress probably isn't technically the safest, but admit that I've done it and felt fine with it at the time. The mattress did lose air over the course of the night, causing DD to roll even more close to me, but she typically is right in my armpit all night anyway so it wasn't like she was rolling from her back to her face, but more like from her back to her back and a little bit of her side, pressed up against my side. I didn't feel like there was any danger of squishing her because we were so much heavier than she is that she was actually thrust up by our weight pushing down. There is no way she could have gotten underneath either of us at all. (For this reason, I think your LO on the mattress with you is probably better than on his own mattress, where he would sink down if it deflated.) If it hadn't felt safe and comfortable, I would have deflated the mattress and slept on the ground (we were tent camping).
Mama to my sweet pea:, can't believe how fast she's growing!