
Exped
MegaMat Series
Car camping comfort king; warm and durable.
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My current pad is an Exped Hyperlite (discontinued) with an R value of about 3.2. I have used quilts for 15 years. I do not tie the quilts to the pad. Always a side sleeper, unless I take my hammock. The quilt you use must be wide enough to tuck. I am claustrophobic, so need to get out easily. And I always sleep warm, tucked in. Many nights were below freezing. Big Agnes bags that have the pad pocket seem to lead to cold people, because the pad holds the bag wide open. Having the ability to tuck whatever you use for insulation around you is important because you warm up the insulation with body heat, air space will make that harder.
If you get a Big Agnes it will squeak against the tent floor all night when you move. I use Exped. Not completely noiseless, but built differently than the Neo pads and not a Big Agnes. I have a discontinued Hyperlite, will replace it with an Ultra when it develops too many leaks just as I did the Synmat. I wish they still made the Hyperlite.
If you get a Big Agnes it will squeak against the tent floor all night when you move. I use Exped. Not completely noiseless, but built differently than the Neo pads and not a Big Agnes. I have a discontinued Hyperlite, will replace it with an Ultra when it develops too many leaks just as I did the Synmat. I wish they still made the Hyperlite.
I have a previous back injury. I find the Womens S2S Etherlight to be the most comfortable, though the least warm. Next for comfort is the Nemo All Season, as well as the Nemo Tensor. In comfort, they are both just slightly less comfortable than the S2S. Both are warmer than the S2S. I have used the ExPed Hyperlight pad for about 40 nights. I believe this pad has been replaced with the newer version. Mine was a 2.8R value. For me, the warmth was equal to the S2S pad. It was not an uncomfortable pad. It just wasn't as comfortable as the S2S and Nemo pads. I tried the Thermarest NeoAir Xlite. My lower back ached when I used the pad. It just didn't have the support I needed. I wish I could use it as it has great warmth to weight ratios. I used the wide versio pads for each of these, though the Exped was a mummy MW version I would assume what is comfortable for me may not translate to you as your back injury may be different than mine. My injury involved the lower back. I have slept in a hammock a few nights and never experienced back pain.
I have an Exped as well as the bestway one often mentioned here and the zen bivvy one, and the exped is the comfiest and warmest hands down. However I can’t remember which one it is exactly (it’s an old model, now deprecated, but 7 cm deep). Also has by far the best inflation system.
Most will tell you “you need an underquilt”… but if you prefer the little extra structure/support from a pad, like me, then a pad will do JUST FINE! I have an under quilt, but prefer and pretty exclusively use an inflatable pad. I think what works best is a mummy shape with rounded corners and tapered foot end. I use an older exped synmat LW (long wide) mummy shape pad, basically same as current exped 3R pads. It fits great in my hammock (hammock gear circadian). It’s super comfortable, I don’t get any cold spots at my arms or feet. Would also work great if I ever needed to ground camp. .. you don’t “need” and under quilt, if you have a pad that works well with your setup.
I have an Exped Synmat and it's quite comfortable. It's more "air mattress" than my Thermarest Prolite Plus but more comfortable. So much so I'm insisting my wife use my Synmat mattress instead of her existing Thermarest on our next trip. I can handle the lesser one (I hope). I think basically if you're spending some money it's always going to be more complicated than "air mattress". I think OP means a classic vinyl sack filled with air. They tend to have poor support, zero vapor management, and are cold (because air convection inside the mattress takes all your heat and moves it to the ground).
I’ve been using a similar set up for years now. Robens z mat, Exped Synmat and a Criterion sleeping bag. Haven’t had an uncomfortably cold night yet and I tend to camp in autumn and winter.

Exped
MegaMat Series
Car camping comfort king; warm and durable.

NEMO
Tensor Series
Lightweight side sleeper favorite, but polarizing on warmth and noise.

Exped
Ultra Series
Comfortable, quiet side sleeper pad; compact for backpacking.

Big Agnes
Rapide SL Insulated Sleeping Pad
Comfortable with unique side rails; R-value and durability disputed.

Therm-a-Rest
NeoLoft™ Sleeping Pad
Very comfortable; a bit heavy and bulky for backpacking.

Ranked #1
Exped - MegaMat Series

Ranked #1
Exped - MegaMat Series

Ranked #1
Exped - MegaMat Series

Ranked #1
Exped - MegaMat Series

Ranked #1
Therm-a-Rest - NeoAir Xtherm Series