Campmeister Deluxe Insulated Air Pad

If packing space, weight, and cost are all no issue - then the Exped Megamat is the top choice for comfort and warmth. For me, it was too big to pack so I opted for the Big Agnes Campmeister deluxe XLW (extra long and wide) - packs down tiny, really comfortable, and insane thermal value I think R value 7

Best sleeping pad is a 1,000% subjective. Different pads will be comfortable to different people depending on their preferences and sleeping habits, and the most important thing is finding a sleeping pad that is comfortable for you to sleep on. Now, there are **objective** differences between sleeping pads when it comes to things like price, R value, weight, packability, durability, etc. Many of these qualities are going to be directly antithetical to each other (e.g. higher R values and durability are generally going to come with a weight penalty; lighter weights/more packable are almost always going to be more expensive as well as more delicate). You just gotta try to find the pad that feels comfortable to you AND has the best combination of those objective qualities that matter most to you. Personally I've settled on the Therm-A-Rest Neoloft as my 3-season pad and the BA Campmeister Deluxe as my colder weather pad. Those pads are bigger and heavier than a lot of options on the market but they are super comfortable for me to sleep on and are made from more durable materials (75D on the BA and I believe 50D top/75D bottom on the Neoloft) so hopefully the odds of me waking up on a flat pad on cold hard ground are greatly reduced. Although I do also own a Nemo Tensor if I ever feel like I need to go super light for some reason. I am lucky to be in a position to own several high-end sleeping pads to keep around as options for different conditions!

Get something with a super high R rating - higher than you think you need. Look for a baffling system that is either dimpled or vertical. For whatever reason, horizontal baffles don’t have a lot of “give” to them so they are less comfortable for side sleepers in general.  Therm-a-Rest Neoair Xtherm is probably the warmest pad out there (not the highest R rating per se but the most effective insulation system means it is still warmer than other pads with higher R values). It may not the most comfortable for a side sleeper because of the horizontal baffles, however. But this is the pad you want if you want to prioritize warmth. If you want to prioritize comfort, Sea to Summit Ether Light XR Pro will probably not sleep as warm but will be more comfortable for a side sleeper because of the dimpled baffling system. Nemo Tensor Extreme Conditions is also very warm and only slightly less comfy than the Ether Light.  Exped Ultra 7R is a bit heavier and bulkier but is very comfy for a side sleeper. It uses down rather than reflective film for insulation. So it won’t be quite as crinkly as a lot of warm pads, but I’m not sure if the down insulation is more or less effective in this application.  Big Agnes Campmeister Deluxe is quite bulky and heavy for a backpacking pad but is super, super comfortable and has a very respectable R value of 7.  The other big, bulky “luxury” comfort backpacking pads - Exped Megamat Ultra and Therm-a-Rest Neoloft - are great options for comfort but with lower R values so they may be less warm than you might want.  Other things to consider - even a well-insulated sleeping pad will only stay as warm as your body is able to heat it. The bigger the pad, the more of your body’s heat it will draw away from you. So don’t buy a massively oversized sleeping pad thinking it will automatically be more comfortable. For insulating purposes, something that is only as big as you need it to be will be more efficient for your body to keep warm.  Make sure you take advantage of all the usual strategies for staying warm in the backcountry: Use your Nalgene as a hot water bottle and keep it in your sleeping bag/quilt with at night. Do some jumping jacks or other activity to get your heartrate and body temperature up before going to bed. Make sure you are properly hydrated and getting enough food to keep warm. Etc. 

Get something with 4 inchs of thickness. Us big guys need that level or near to it of thickness. Nemo Quasar is close, same with Big Agnes Campmeister. I have the Thermarest neoloft and love it. I'm also a big guy. Thermarest and definitely the Campmeister are good for those temps.

Big Agnes campmeister deluxe. R7 value 3.5 inches thick. Their long extra wide is 30” wide by 78” long. It’s magic.

Big Agnes Campmeister or the Exped Megamat Ultra. Both are comfy and you can really spread out. Neither is light, but both are worth taking for good sleep.