Camping can get quite cold at night (even in the summer) and will be a lot darker so your 2 year old might want to end up snuggling with you but would be OK with his own sleeping bag rather than climbing into yours. Sleepy bags are fun for pretending to be a wiggly worm in and yes too much wiggling can cause the sleeping bag to roll off the blow up mattress and end up in the corner of the tent with child). Amusing but annoying at 5am with "help mummy l'm stuck". Conclusion - take both. Camping is a lot of trial and error.
If you use a ready bed, but a fleece sheet under the child and a foam mat under the ready bed - because they are blow up mattresses they offer no insulation from the cold ground.
Or you can use foam tiles (the big interlocking play mat ones) as an insulating floor in the bedroom pods.
Personally I think children are better on roll out foam mats or a SIM than a normal blow-up mattress because they can't roll off them and get stuck. And if you have insulated the whole floor with mats, they are still protected form the ground.
I like that #dropzone. I think I'm sold on that or a ReadyBed, it will keep him vaguely in one place! I have visions of him slowly wriggling/headbutting his way across the tent in the middle of the night otherwise!
We have a similar airbed to the one DropZone suggested. They are a good idea. We have a Kelty Woobie sleeping bag, which is excellent and can be zipped up at the bottom to make it smaller. It is better quality than the sleeping bags DH and I use!
We have the kampa airlock and with a sleeping bag it's perfect. I don't think the ready bed would be warm enough personally without extra covers. We just put a fleece blanket under the air bed for insulation