Trestles Elite Eco 20°

Its been 10 years now but I think between my wife and I we brought a down 15 degree and maybe an older MH 15 degree synthetic that had lost a bit of its loft. I don't remember who used what but neither of us were ever cold. I think I have the same Marmot bag you are referencing (terrible with remembering model names) that I use on occasion (if its damp, or if I don't want to get my expensive down bag smokey, etc). I have no complaints with it, but I kind of recall the consensus being a little on the cold side for being rated 20 deg and really should be more marketed as a 30 deg. I'd have no reservations taking it up there that time of year but just go into it viewing it that way. Would it be different enough from your quilt to justify the cost? Can't answer that as I've never used a quilt.

I would steer clear of Amazon unless you find something from a big-name outdoor brand on there (marmot, big Agnes, mountain hardwear, Nemo, to name a few). A no-name Chinese brand bag is probably not going to meet quality or temperature expectations. Your local REI would be a good resource. Their house branded stuff is trustworthy. SierraTrading (TJmaxx for outdoor gear) usually has a decent selection of name brand options. I have a 20° marmot bag from there that was $80. Buy a bag that’s at least 10° colder than the temperatures you expect to encounter. Caveat is that like most camping equipment, no modern sleeping bag is going to be truly BIFL, they are wear items at the end of the day. In a hammock, the compression of the bag underneath your weight will always hinder the insulation ability. This can be mitigated with a foam or air-filled sleeping pad. You may have to experiment to find one that fits your hammock, fits your dry bag, and keeps you warm enough, so I would say this is something you could grab on Amazon for ~$20. Edit: didn’t register your parts about the under quilt but yeah it’s just a matter of spending money and experimenting, unfortunately

I'd been using a Marmot for 30 yrs, what they called a 10-20 30. Don't remember the price but it was the most expensive thing I bought for a very long time and glad I did. There were not as many choices back then and I don't think they are the same now. Point is it was annoying when it was warm. Couple of years ago I got a Feathered Friends Flicker 40. It's a hoodless sleeping bag that can also open all the way to a quilt. (no it doesn't attach to a pad) Had that down to mid 30's cowboy camping in the desert and was fine with a puffy on. I had wanted a 30 but out of stock. This year sold the 40 and got a 30 for a trip to Iceland in July. I'm very happy with it; works well across temps. Combined with the Marmot gets me down to 0. Since it is a bag when I want it's less fuss than a lot of the quilts out there. (love the draft collar and the foot closing completely). You can rent one and they will credit up to 2 nights rental cost toward a similar purchase. May help but likely incur some extra shipping costs unless you're in their area.

For casual three-season camping around 0°C, synthetic’s way easier on the wallet. Marmot Trestles or Kelty Cosmic Down alternative bags hold up fine, and you don’t freak out about melting water or sweat ruining insulation.

Used Marmot Treasles Elite Eco. You can find these used on eBay and REI ReSupply for around $50 or less often.

Naturehike Mongar 2p. If you really can get a Marmot Limelight for under $150 definitely get that over the Naturehike (DAC aluminum poles and a lifetime warranty are primary reasons). For a bag I would look for a deal on a Marmot Tressles Elite Eco. I have seen the older models on clearance for under $100. These pack down much smaller and weigh far less than traditional synthetic bags. If you can afford a down bag go for. Paria Outdoor Products Thermodown 30 or 15f. Otherwise if you are with used try to find a quality down sleeping bag. Cots under $75 go with a Naturehike, iClimb or Kingcamp cot with aluminum poles and legs. Aluminum cots pack down way smaller and weigh significantly less than steel. For the sleeping pad I would recommend a knockoff of the Exped MegaMat. Semi inflating mats are way higher R value than the junk Intex and Coleman air mattresses and way more comfortable. A budget alternative to the MegaMat would be th Stoic Cloud or Cloud Lux or the Hikenture semi inflating mat. These are 3-5" thick and feel like sleeping on a bed at home. Combine them with a cot and it's pure luxury.

Marmot Trestles line are good deals on good bags. If you’re younger, just get a blue foam pad.

Western Mountaineering, Feathered Friends or Marmot for bags. Enlightened Equipment, Hammock Gear or Katabatic for backpacking quilts. Not cheap but quality and comfortable.