
NEMO
Disco 15 Series
Spacious for side sleepers; bulky, temp rating optimistic.

Running these analyses costs money. Buy through my links to help keep lights on! I may get a small commission.
Splurge? 6 years ago, 2 EE convertible quilts. One xl/xw Apex 30° and a 950 down 10°. - my Best. Investment. Ever.- They work independently or together as quilts or sleeping bags... Can be zipped together to make one giant 2p sleeping bag. The Apex is an xl and the down bag will fit inside of it, added a liner for full 4 season in most of North America. Basically have 7 different systems with these two pieces. All together for around 4 lbs.
Splurge? 6 years ago, 2 EE convertible quilts. One xl/xw Apex 30° and a 950 down 10°. - my Best. Investment. Ever.- They work independently or together as quilts or sleeping bags... Can be zipped together to make one giant 2p sleeping bag. The Apex is an xl and the down bag will fit inside of it, added a liner for full 4 season in most of North America. Basically have 7 different systems with these two pieces. All together for around 4 lbs.
Enlightened Equipment can suck my entire asshole.
[EE are racist/fascist](https://www.reddit.com/r/Ultralight/s/afJAagvKix). It’s worth noting that they promised to course correct but I just checked and one of the posts that they were specifically called out on (with screenshots) for interacting with racists is still up. That aside, the convert is probably the worst quilt you can get. For one, the baffles are super long, which will promote down migration and cold spots. It does not have differential cut, which boosts performance and down stability (and at almost $700, should come as standard). EE products are also limit rated, so you better go at least 10° colder. A 0°F Convert, x-short regular is 800g and $670, which becomes 880g and $720 if you throw in a hood. A short WM Versalite is lighter (850g) only $35 more ($755) and is considered among the best bags you can buy. There is absolutely no reason to even consider EE.
Try Enlightened Equipment. The Conundrum and Convert come in a x-wide 70" shoulder girth and extends down a ways toward the hips at that width. Conundrum has a 3/4 length zip and Convert has a full zip opens like a blanket. You can order them in 10, 0 and -10F warmth ratings. You would need to add a hood because neither one has a hood. Another possibility is Western Mountaineering Cloudlite, although it is a 15 degree rated bag. It has a 65" shoulder and 68" hip girth. Conundrum and Convert can be used a quilt unzipped and might work if you can learn to stay warm using a quilt.
I came to suggest a quilt from EE, glad it's already top comment. I love love love my EE Convert quilt with Apex synthetic insulation for both sleeping in a hammock or on a pad in the tent.
I have a Convert quilt from Enlightened Equipment with Apex synthetic insulation. Recently took it on a backpacking trip in Colorado and my buddy who I hadn't been on a trip with in years remarked that it must be the most packable/compressible sleeping bag ever haha. And I'm sure if it had the down insulation it'd be even more so. One thing to consider, however, is stuffing your sleeping bag or quilt directly into the pack, instead of stuffing it into the stuff sack and putting that in the pack. I switched to the former method a few years ago and I find it gives me quite a bit of extra space in the pack. For my BWCA trip crew (3 guys), we now stuff the inner part of their tent, their two sleeping bags, my hammock and my under quilt and top quilt (the EE Convert) all directly into the bottom of the big dry pack we have, no stuff sacks. The loose stuff method saves a lot of room.
I also move around a lot when I sleep and found a quilt to work much better for me. I use an Enlightened Equipment Convert. It looks like it is a bit above your budget, though. I agree with u/Trogar1 that a good sleeping pad can make a world of difference. If you run cold, you could look at insulated pad and I would recommend an inflatable pad if you are a side sleeper. I found the extra few inches of thickness really help keep my hips from getting sore/cold vs. a thinner pad.
I bought a used quilt on marketplace. Enlightened Equipment 40 degree.

NEMO
Disco 15 Series
Spacious for side sleepers; bulky, temp rating optimistic.
Hammock Gear
Classic Burrow 20°F
Budget king; very warm but heavier than ultralight.

NEMO
Disco 30
Spoon shape for side sleepers; prone to zipper issues.

Western Mountaineering
VersaLite
Durable, very warm; premium price, too hot in summer.

Katabatic Gear
Alsek 22°F Quilt
Versatile 3-season quilt; secure pad attachment, high price.

Ranked #1
NEMO - Disco 15 Series

Ranked #1
Kelty - Tru.Comfort Doublewide 20
Ranked #1
Enlightened Equipment - Revelation APEX

Ranked #1
NEMO - Disco 15 Series

Ranked #1
Feathered Friends - Egret UL 20/30

Ranked #1
NEMO - Disco 15 Series