Mt preference is a closed cell foam mattress, also durable, fool proof, and versatile. I am a side sleeper and have been using one for years. They can easily be cut down, if you desire, to save weight.
Thanks for reaching out.
I would recommend an inflatable sleeping pad that has at least 3" of thickness to it. As a side sleeper myself, I found the Big Agnes sleeping pads tend to be more thicker and comfortable. The Big Agnes Q Core SLX has a 3.5 inch thickness, giving plenty of cushion for your hip bones and other pressure points. However, we have a lot of other pad options at rei.com where you can even filter the settings to see sleeping pads with various thickness's. Here is a link to all the pads we sell that are 3-4.9 inches thick. I would avoid any thickness's less then 3", as those accommodate more back and side sleepers.
If you would like to look at other options and discuss other possibilities check out our virtual outfitting services.
I hope his helps.
I have a big agnes air core ultra, a big agnes air core ultra insulated, and a /thermarest neoair xlite (women's version). I like the air core ultras, and have used them many times without issue. I recently switched to the thermarest for lower weight and like it too, although I've only used it two nights so far, so I'm not sure about the durability. I'm a side sleeper like you.
Hi @MDR .
I am also a side-sleeper, and I agree that the inflatables suit me the best. I use a Klymit insulated Static V. The closed cell pads @hikermor mentioned definitely have their uses and benefits (like never getting punctured and leaking), but they are not as cushiony. When car camping, and/or in cold weather, I'll use a closed cell foam under my inflatable for extra protection and insulation.
A friend of mine has a Thermarest, which he likes, but it squeaked every time he moved. Something to keep in mind.
One other thing to consider is to get a sleeping bag with an integrated sleeve to contain your pad. It's not a necessity, but if you move around a lot, it'll help prevent your from rolling off the pad.
I recently invested in a Nemo Switchback, and even as a bony side sleeper and I haven't had any issues yet. It's a closed cell foam pad and it isn't very thick, but it's warmer than you'd think and is very light. I prefer it over the inflatables because it's quiet. Definitely just a summer to early fall pad though.
Probably as many opinions as there are different pads but in mine as a side sleeper...
The all round best lightweight inflatable pad is probably the Thermarest xLite. It it light weight (12.5 oz regular size), reasonably robust, easy to repair, reasonably comfortable (2.5 inch), reasonably easy to inflate and is reasonably warm (R 4.2). Thru hikers have put 1000s of miles on these things to good effect. Other pads are more comfortable but don't make the trade offs as well. Some people find xLites a bit noisy (crinkly like a bag of chips is the usual complaint) but if they are, it has not bothered me. People also say they quieten over time and that the latest version is quieter but since it doesn't bother me in the first place I couldn't say.
Optionally, you can combine this with a Thermarest Z-lite Sol(use sliver side up) or Nemo Switchback (use silver side down) to extend the temp range ~+R2 for winter use or shoulder season alpine use. Or in general with an 1/8inch EVA foam pad for some ground abrasion protection and a small boost to insulation (maybe + R 0.5). Doing so also gives you a convenient day pad and insurance against irreparable failure.
There are very light weight (Uber Lite R2.3) and winter variants (xTherm R6.9) of this pad design if either of those are your thing. They have different but also well chosen tradeoffs. Also torso length (for minimalists), wide (~ 25inch better for back sleepers), long and "women's" ( R5.4, if you are shorter and like more warmth).
A possibly more comfortable pad is the thicker (3 inch) NEMO Tensor but it is heavier and even the insulated version is not as warm (R 3.5). I have not used this pad.
Another pad I have not used but I have heard good things about as far as comfort is the even thicker (4 inch) Sea to Summit Ether Light XT Insulated (R3.2) Air Sleeping Pad.
Generally the bigger and thicker the inflatable pad the more breaths it takes to fill. These days there are pump sacks which some inflatable pads come with which are quite quite light, sometimes multi-pupose and work well instead of blowing. The NEMO vortex is particularly effective and light but single purpose. Generally these are proprietary to the brand due to valve differences (The Nemo vortex works with the old Thermarest valve but not the new one). However, it is something of a myth that blowing into a pad by mouth encourages mold..one of the reasons people use to justify a pump sack. While this may happen, people who have cut their supposedly moldy xLites have found that "mold" they are seeing blocking light through the pad is just the silvering on the internal mylar layer. Where the light shines though, the mylar has abraded off after extensive and repetitious folding and unfolding. This will make the pad less warm but there is no mold. Pads that contain foam (eg: self inflating) or down insulation may possibly be prone to mold.
For the more ascetic, as @hikermor says, a closed cell pad alone can be enough even for side sleepers but they are very hard to use alone and it is an acquired taste for most people. They are inexpensive and robust to the point of being nearly indestructible in a backpacking context and give you a convenient day pad. They do compress with extensive use. Their main drawbacks (apart from being hard) are being very bulky and generally having a R value of less than 2. You will almost certainly need to carry it on the outside of your pack. The Z-Rest and Switchback Sol I mentioned above are better than most of this type since they fold relatively compactly and have R values of about 2.