We've always done something like Val - we had old foam camping mats from our backpacking days and the children were fine sleeping on those -seemed to be cosy just with their sleeping bags and sometimes an extra blanket. Will probably upgrade this year to self-inflating mats for them but the foam mats have done a good few years.
We camped with DD2 from when she was about 6 months.
When little she was in a baby gro, in a fleecey suit inside a baby sleeping bag (the sort of things with arm holes - designed for normsal sleep at home). Maybe a blanket as well if cold) she would start off on an old Karrimat, but as breatsfed would always end up on the airbed with my wife anyway. That was basiucally the arrnagement for the first couple of years camping, then last yueasr (3 1/2) she progressed to a small size Vango sleeping bag, ona slef inflating mat (she is just the right size to fit on my old 3/4 length Thermarest). They do sometimes slide off them, but it's never a problem for them it seems
Re the Ready Bed. We had one which we bought for DD1, not especially for camping. They are ok, but overpriced (we got ours half price IIRC, they aren't worth the full price) DD1 use dit for camping, the level of insulation is low, though with a fleecy oversuit daughter was fine, also she tended to slide off the side anyway. We never used if for camping with DD2
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.