In 2012, I used a thermarest when I took my 9000 mile trip. It worked well, but it is bulky. So in 2013, I switched to a Big Agness sleeping bag and air mattress. The reason was two-fold. The BA bag has a pouch in which the mattress slides. This keeps you always on top of the mattress, and reduces bulk in the bag. The second reason is that deflated, the mattress takes about as much space as a one liter water bottle. Quite a bit less than the thinest thermarest.
A few nights ago I woke up on the ground. The mattress was flat. I've been trying to find the leaks and fix it since then. Yesterday I finally drowned the thing in a utility sink and found the leaks. Today I attempted repairs. I will find out in a few hours if I was successful. If not, I'll try again.
It's not just that the ground is hard (it is), but it is still cold as well. Sleeping on cold and hard ground leads to a bad experience. When I was younger, I slept out quite a bit, but that was 46-8 years ago. I'm no longer that resilient.
In fact, I remember quite distinctly in 1969 while camping in a tent in the rain at Ipsut Creek Campground that I vowed to not sleep on the ground again. That vow led to the acquisition of the old '61 VW van into which I built the camper. That camper certainly kept me off the ground and out of wet tents as Karin and I drove it around the continental USA in the summer of '72. I may be ready for something similar once I'm done with this trip. Or even before then.
Expedition grade equipment is really difficult to find. Moreover, it is generally heavy, because expeditions are usually 4 wheel vehicle based. When you ride bikes or motos, weight really matters. So I bought good quality gear. Looks like I should have found something tougher. At least I know that when all else fails, I have my USMC poncho liner to fall back on. Actually, it's not really a poncho liner. It's whatever they issue now instead of a poncho liner or shelter-half. If you don't know what a shelter-half is, you are not Old Corps. (Inside joke for Marines. Semper Fi).