I always take a self-inflating hiking mattress with me even in 1st class as the seats tend to be lump and the mattress pads are only about 1 cm thick. The brand I find is quite good is thermarest evolite, which weights very little, self inflates, and then maybe 5 puffs and its fully inflated and after sleep it rolls up into a small quite small sack that you can go in your carry-on or attach to its handle when entering and leaving the aircraft. Its been very worthwhile, even if it does arouse some interest from other passengers. Sometimes I also take a hiking pillow as well, as most airline pillows are flat (unless you can forage for extras in unallocated seats).