I have used a climbers-weight inflatable thermarest pad for 15 years on more than a hundred flights in BE. They are fabulous - especially if you like to sleep on your side. It supports the hips and shoulders much better than the seat does. I have used it on trains, in airports during long delays, and to give some relief from the miserable mattresses in remote areas of Asia. The inflatable ones are much more comfortable and convenient than the folding ones the OP describe. The really light kind roll up to something a little larger than a liter water bottle and I keep it in my carry on with a thermarest pillow. They self-inflate to just about the right amount, close the valve, and you have a bed. I have gotten countless comments from FAs, pilots, and my seat neighbor, and more than a few offers to buy it from me. It is slightly too wide for a typical seat in Y though - it will extend into the next seat unless you are in a bulkhead/exit seat with the fixed armrests. But I never fly without it.