
Exped
MegaMat Series
Car camping comfort champ, but some side sleepers find it thin.

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Personally I am UL-allied and accommodate my cranky needs despite that ruining my BW. So will not react in horror. I haven't tried this but my wife and I use a Duo and love it; personally I'd try the shorter one; and if it doesn't work out swap up. (I still use the crinkly Thermarest UL thing and you could carry that in addition to the short Ultra and still be a few grams shy of the long one lol.)
Thermarest neoairs are too loud and crinkly for me. Rab style of mattress doesn't do well for me as a side to belly sleeper. Nemo is my pick because the only air pads I've kept are Nemo. An astro non-insulated pad is my summer pad with an older cosmo insulated pad being my 30 to 55-deg pad.
I'm also from the UK. I have been through a lot of tents and air mattresses trying to find the right duo! Right now I have the Thermarest Neo and the Alpkit Jaran. Perfect duo!
Exped megamat for car camping, thermarest neoair for backpacking
If I were you I’d get the best car camping mat available. 50 nights year deserves comfort! Go get the Exped MegaMat. Then get a backpacking sleeping pad. If you got money (you don’t mention budget yet) - get a ultralight one like the Therm-a-Rest NeoAir. Ball out. Plus it packs super small when you aren’t using it. 2 pads is really the answer. Trying to get one for both you’ll end up unhappy on both.
As a side sleeper I sleep much more comfortable on pure ccf than on air mats. Had a Neo Air but after it failed for the third time in a row I bouhgt a Ridgerest and expected quite hard nights. But I slept better than ever. I think it's because I'm much more stable and don't need my muscles all night long to keep myself stable.

Exped
MegaMat Series
Car camping comfort champ, but some side sleepers find it thin.

Exped
Ultra Series
Lightweight side-sleeper comfort, but a bit pricey and bulky.

NEMO
Tensor Series
Ultralight side-sleeper comfort, but slippery and prone to leaks.

Big Agnes
Rapide SL Insulated Sleeping Pad
Comfortable with side rails, but heavy and warmth claims disputed.

Therm-a-Rest
NeoLoft™ Sleeping Pad
Very comfortable, good service, but 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