NEMO - Riff

My advice: NEMO women's Disco 15. First off, sleeping bag temps (ISO/EN) are rated for slight discomfort. If you want to be mostly comfortable at 30F, you get a 30F bag; if you want to be warm and toasty, you get a 20F bag. If you think temps may drop into the 20s but may realistically be 30s, you should get a 20F bag; if it hits 20F, you're fine but you'll otherwise be toasty. Women's bags are rated at the Comfort rating which is toasty and nice for a warm sleeper, slightly uncomfortable for a cold sleeper - which is the assumption for women. Also what it sounds like you may be: a "cold sleeper"/someone who likes to be warm at night. Know that you can - and should - try other gender bags for fit as you may find better fits across genders. But keep in mind there is ~10F temp difference between men's fits and women's fits (men's will be colder for cold sleepers, women's will be warmer for warm sleepers) and so don't just trade 30F for 30F. In your case, use the "Comfort Rating" as your slight discomfort temperature and adjust from there. Know also that this may work against you price-wise; they do not price based on fill, they price based on advertised temp. So a women's 30 will be the same warmth as a men's 20, but will be priced as a 30, not as a more expensive 20. So the Magma and the Disco may not be warm enough for what you're looking for. Of the listed bags, they'll fit in order of how you listed them: Disco will be the widest, then Big Agnes, then the Magma. The Magma is a true backpacking mummy and won't be ideal for a side sleeper. The Disco has extra space in the shoulders and hips which are ideal for getting on your side in the bag. So for a cold sleeper who sleeps on their side and is likely to have some 20F but maybe mostly 30F nights - NEMO Disco 15. Should check all of the boxes. The one big difference between the NEMO and the Magma is down fill power, which also impacts compressibility and weight. Magma is an 850 while the Disco is probably around 650-700. If you want a similar fill power bag go with the Riff 15. 850 fill down also warms up quicker because the feathers are smaller. It will also probably be more on par price-wise with the Magma. The Riff has all the same features as the Disco though may have a slightly slimmer shape. If you can, go to your local REI and get in each one to see which are comfortable and which are not. But based on the info you've given, I'd suggest either a Women's NEMO Disco 15 or NEMO Riff 15.

As a side sleeper who turns like rotisserie chicken I would highly recommend quilts. If you still want bag then maybe Nemo riff 15 could work. Quilt is around 1/2 to 2/3 the weight and way more room to turn and toss and no hood helps you with side sleeping. You can get -2 Celsius comfort quilt under 300€ from liteway: https://liteway.equipment/quilts/simple-quilt-870-fp-10d It's Ukrainian company. Edit: there are also sleeping bags made for side sleepers like this: https://www.amazon.de/-/en/Big-Agnes-Sidewinder-Sleeping-Bag/dp/B0C5D7V47C

Nemo Riff 15 might be a shout. I use a sea to summit reactor liner with it and I'm roasting. I've had that at -10 without the need to layer clothing inside

Depending on your specific needs for temps, weight, and filling I'd recommend, Nemo's Rift, Forte, or Tempo bags. They have a "spoon" shape (extra space around knees and elbows and tapers around the waist and feet) rather than mummy shape. They're designed to feel less restrictive and I've found them to be so. Of course the bag will take up a bit more space than a mummy bag, but it's better than a regular rectangle bag. I have the Tempo and I think it's good for regular backpackers and I really like it. They're common at REI too so you may be able to try it out.

For clarity - The Riff (and Disco) are down. While the Forte and Tempo are synthetic. Their spoon/peanut shape is definitely very popular with side sleepers, or people who sleep angular or toss and turn. Much more forgiving than a regular mummy, without the draft issues of a quilt. Recommend people getting into quilts, to buy a wide one. This will help mitigate drafts. You mention REI, all of their sleeping bags now come in "wide" versions. Still a mummy for the most part, but about 5" wider than a regular mummy. Their Magma is an excellent bag, as is their Magma quilt, but it's only rated to 30 degrees.

Love my Nemo bags and always recommend them. Great product, great customer service and repair, and good price. And they make bags that are specifically cut to minimize dead space but accommodate side sleeping. https://www.rei.com/product/228442/nemo-riff-15-endless-promise-down-sleeping-bag-mens A few other things to keep in mind: - A great bag is useless without a pad. Make sure you factor that into your investment if you haven’t already. - A 20 degree bag might keep you safe in 20 degree weather, but you won’t be happy about it. I want a 0 degree bag if camping in anything below freezing. (But I am a small-ish woman who runs cold.)

Honestly I bought a Nemo Ramsey 15 a number of years ago and it was terrible, enough for me to avoid Nemo sleeping bags. Maybe it was just that model or something but I forever woke up looking like a chicken covered in tiny feathers and right from the get go it was clearly understuffed. It was much colder than a number of my friends 9-15 rated sleeping bags. I've since got a different bag that is rated to the same temperature after learning more about fill weight/power and it's clear that Nemo bag was a piece of junk. The kicker is Nemo seems like a great company and even sent me another one assuming the one I got was a lemon, and it was the exact same thing. I don't think I'd go back to Nemo for a sleeping bag

It’s all about a good sleep system. I have a 15 degree Nemo bag and an XTherm pad. Throw in a hot water bottle and I’m toasty all night. Just sleep in a base layer.

I love my down 15* Nemo bag. It's a huge warmth difference compared to my synthetic 25* Nemo.

Nemo down sleeping bag. My most expensive and by far my favorite sleeping bag.

Nemo down 15F is my favorite. I felt warm sleeping when outside was below 30F. Wait for the next sale in REI you can snag it for nice discount.