I haven't worn a dry suit flying, but they are fine for dinghy sailing which is a very active sport. We wore the fabric ones with varying amounts of fleece underneath for insulation - there is no warmth in the suit itself.
You don't want a diver's dry suit as they are designed to take pressure from the breathing set.
If you want comfort look for one a breathable one, otherwise el cheapo will do fine, but do look after it properly and replace the socks / seals if they start to deteriorate - it's an easy job to do yourself. I used to keep mine hanging up so it was dry and not getting 'pinch points' squashed into it.