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

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Thermarest Luxury Map or a similar plush camping pad. They don’t require a pump, roll up more compactly than an air mattress, and are much more resistant to popping.
A thermarest Luxurymap Xlarge offers 3 inches of max loft, but I like it a bit soft, so I don’t inflate it hard. To raise the comfort factor, simply wrap it in a fleece blanket. Instant upgrade from R6 to something way way warmer, for a few $. I take my full size cotton pillows too, and at -25 deg C, you can imagine how cold these get. Again, I wrap a fleece blanket around the pillows, and it provides superb insulation. Don’t waste money on expensive gear, when there are superb cheaper options that work. Just my 2 cents. They are also useful for general warmth. I always pack two fleece blankets for my winter camps. Toasty warm down to -25 deg C, or -13 deg F. and my trips are done in a 3 season, MEC Wanderer 2 (zippable mesh inner tent, not a true 4 season tent), using a Thermarest Luxury Map XL inflatable pad, one fleece blanket wrap, and an MEC hybrid mummy bag rated to -20 deg C, which works as I sleep warm anyway. Empty your bladder before crashing, to stay warm. You won’t need anything else. If you aren’t backcountry camping, those jigsaw puzzle style square rubber mats (children play mats) can be setup inside the tent. Super insulation from ground heat loss. Costs about $30
Will be hard to find something at that price point, so might want to check for used gear or keep an eye out for discounts or sales. What I use/can recommend: 1. Zempire low profile cot with any sleeping pad on top (note: weight limit 220lbs) - nice, sturdy, nice to be flat and up off the ground 2. REI Camp 3.5 insulated sleeping pad, I think this was discontinued (mine is old) and the Camp Dreamer is the new model name, soft, self-inflating, thick/insulated 3. Thermarest Luxury Map insulated sleeping pad, soft and comfy, insulated, self-inflating Make sure you have a decent pillow or pillows. I just got the Klymit drift camping pillow and have been testing it out at home. It's amazing, feels like a real pillow, and I can't wait to use it at camp this year.
I assume you are car camping or have some kind of sled or pulk or vehicle to help carry your gear. Layer: - closed cell foam mat/sleeping pad - insulated air sleeping pad with R-value at least 6 (the higher the better -- I have a Thermarest Luxury Map that is awesome) - pillow (something that is a real pillow, not air filled, is preferred - for camping pillows I am loving the Klymit Drift, but any small pillow could be okay) - warm sleeping bag rated as cold as you can get (I have the US military modular sleep system that someone else recommended and it's definitely heavy, but very warm, and if you get all 4 pieces the 4th is a waterproof bivvy, which is nice, especially if it's snowy, to keep your bag dry) If you get cold in your sleep you can wear wool socks to bed and then put on down booties over your socks. Wear fresh thermals or base layers to bed, regardless. A puffy jacket, knitted hat, and/or Buff can also be worn. Add an extra fleece or wool blanket if you're desperate. I've never done it, but also some people say to sleep naked to let your body heat warm up the sleeping bag. If you do that, put your clothes in the sleeping bag too so they aren't freezing in the morning. Oh, and you can pre-warm your sleeping bag with a hot water bottle or a Nalgene filled with hot water. Especially nice by the foot area.
My wife just upgraded us to a Hest and it was positively luxurious! One caveat, It does take up a lot of space, especially when compared to even the thickest of the self inflating mats. We had been using two Therm-A-rest Luxury Map 3s, tucked together in a fitted sheet, which was serviceable, but just okay. The Hest, on the other hand, was about as good a night of sleep as I get these days. Zero complaints on the sleeping experience whatsoever; Cloud-like.
For car camping I use the therma rest luxury map in the cold. I'm a scoutmaster, so yes, car camping in the winter
I gave up and went out and got the luxury map. I was tired of being cold. It has the best r value. But I'm not winter backpacking, I'm car camping in winter
I've had thermarest since their inception. Great product
I have forty year old thermarests.
I've always had great luck with thermarest
I'm a side sleeper and use a Therm-a-Rest LuxuryMap, its 3 inches thick and the regular is - 20 x 72 Inches, that might fit your needs.

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