Therm-a-Rest - Z Lite Sol

Most closed cell foam pads will be lower R value but can easily get 2 to reach about the same. They tend to not be as comfortable though. Thermarest Z lite has been one of the better that I've seen, but most closed cell foam pads are about the same. I'd make sure to check the dimensions so that they work with you/your pack system.

Z-Lite (6 panels) with an 1/8in ccf pad from atom packs underneath. I figure this comes to an r-value of about 3, fine for me down to about 2C. I sleep in some smartwool merino leggings to keep my legs warmer as they’re off the end of the foam pads. All of this coupled with good site selection on thick grass or pine needles under some tree cover to help with trapping some heat around the tent and I’m comfortable. Different story in winter.

We have a similar setup, but my wife and I share a double sized down quilt (EE Accomplice) on two air pads and our dog has his cut down ZLite and synthetic Kifaru woobie. Our dog (heeler) is about 40lbs. We are vigilant to keep him from getting on our uncovered air pads. Our quilt more or less covers our two pads, so it adds a layer of protection, but we insist that he stays in his ZLite as much as possible. We've gone out dozens of times and only lost a pad once when he was young and tried to bolt after a goat.

Have you considered a camping cot? There are a lot of ultralight options now which are about the same price as a good sleeping pad for side sleepers. The only difference being is the weight, you’re looking at around 1.5kg for a cot bed which would be double the weight of a sleeping pad. For me, the extra weight is worth it for the comfort. For context I’ve tried Therm-a-Rest, Big Agnes and Nemo mats. If I’m going for comfort, the cot bed wins every time.

Z lite. Only about $50 and works great even in wet weather.

That's still not true though. An X-therm weighs 16oz and has a R value of 7.3. Whereas a z-lite weighs 14oz and has a R value of 2. Even if we assume that foam pads perform above their stated r value you would still need multiple to match the warmth of a single inflatable.

Second this. Ridgerest or zlite closed cell foam pads are great for kids and actually pretty comfortable and sturdy. 

Important to know from the start: I have scoliosis as well as a lingering low back/hip injury, and at home I sleep on a probably-too-soft mattress. But I don't have any of the problems I mention below even when I sleep in a different bed with a different firmness, such as while traveling for work or family. My setup as of last year's season is a Therm-A-Rest Z Lite Sol underneath the Big Agnes Rapide SL inflatable pad (standard length, wide width). In other words, I'm not laying flat on the ground by any means - there's plenty of cushion from uneven or firm ground, and I haven't had any temperature issues (I pair these two pads with a now-discontinued Sea to Summit down bag that's plenty cozy). The Big Agnes pad was new last year, after multiple seasons attempting and failing to make a thin Therm-A-Rest Trail Scout work with the Z-Lite (I would anti-recommend the Trail Scout for this and other reasons). But this current setup isn't working very well, either. On some nights I found myself waking up with a leg or two numb on some nights because of some position that had me cutting off circulation. (This happens at home occasionally when I'm sitting flat on the floor, but rarely when I'm sleeping or lying flat.) Even though I played around with the inflation level of the Big Agnes pad, as I was worried it was maybe too firm at full inflation, that didn't seem to help much. I also prefer to sleep on my stomach, and I haven't figured out a backcountry pillow option that's flat enough to keep my neck at a comfortable angle without being non-existent, as sleeping directly on my arms puts them numb too. Out of desperation, I tried bringing my flat-yet-not-paper pillow from home for a trip last year, which feels embarrassing to write because of the pillow's weight and bulk, lol. If it had worked, I would make adjustments to my kit to bring it every time, but it didn't really fix the setup (which is probably for the best for the rest of my packing list), so I'm back to the drawing board. Given all this, I'm feeling nervous about this season's upcoming trips, as I'm not someone who functions well on a lack of sleep. I'd prefer to try and adapt my current setup before I buy new stuff, too, as these are otherwise high-quality products that I think will last a while, if I can make them work for me. For folks who have finicky backs, or sleep in ways at home that are harder to comfortably do out on trail, how do you adjust your sleep setup for overnighters? What might I change here that will help me sleep better while on trail and thus have a better trip overall? I'm considering the Nemo Fillo Elite - can any stomach sleepers attest to this or other semi-inflatable pillows as being worth the buy?

Throw a thermarest on top of a Walmart foam pad lol save yourself some money on the process. Otherwise I would just stick to Thermarest.