Help picking a bag

Quilts unquestionably dominate sleeping bags in hammocks. I would recommend reading "Hammock Camping" by Ed Speer. Your options for warmth are vast. Speer Peapods and top blankets, Jacks R Better Over and Underquilts, or any quilt with a sleeping pad would work well. underquilt are far more comfy than pads in most peoples experiences including mine. A Jacks R Better 3 season set would do you well, although its a bit pricey. If you want to go on the cheap, a speer top blanket or JRB No Sniveler and Speer SPE (segmented pad exteneder) would be good and lighter, but less comfy.

I highly recommend using a quilt instead of a sleeping bag. A sleeping bag is a real pain to get into while laying down in the hammock, and the bottom insulation from the sleeping bag will give you no benefit at all because it will be very compressed. (I used a +15F sleeping bag in +27F weather and froze my butt off, almost literally.) For ‘warm’ temps (above freezing) I use my Jacks R Better (JRB) Nest down quilt (20.2 oz) as a top quilt. If you want to make your own synthetic top quilt, check out the Ray-Way quilt; that’s the basis for my cold-weather top quilt. (Ray-Way is closed for a few months.) There are other good quilt vendors, and you could also just unzip a mummy bag.

The only benefit of using a sleeping pad inside the hammock is that when you wake up cold in the middle of the night because it has slipped out from under you, you can work up a sweat arranging it properly again. Otherwise, you will probably want to use under-hammock insulation. There are three systems that I use. For temps down to 0F I sling the JRB Nest as an underquilt (the Nest is designed to be Hennessy compatible) using the JRB Suspension System (2.0 oz). It works fine above freezing too, although I add the JRB Weather Shield Bottom (9.5 oz) in case of blown rain. For temps above freezing I use the Hennessy Hammock SuperShelter underpad and undercover (21.3 oz for Explorer size). Note that this is actually a bit heavier than the JRB Nest and doesn’t pack as small, so if you can afford it a JRB Shenandoah Summer Quilt (claimed weight 15oz) is a lighter and smaller underquilt. The third system is the cheapest, lightest and also probably simplest option for temps above +40F: use a JRB Weather Shield Bottom to suspend some sort of insulation against the bottom of the hammock. I’ve slept warm enough in a hammock in the temp range you mention using only a Gossamer Gear ThinLight 1/8″ sleeping pad (2.5 oz); the 1/4″ wide/long version currently available might be a better fit. An alternative would be cheap 1/2″ open-cell foam from some other source. Open-cell foam does tend to conform a little closer to the under-side of the hammock.

There are many other insulation systems as well, but between the JRB options and the Hennessy solution I haven’t needed to look further.

Gabriel, I don't really have any thing new to add but just wanted to join David and Douglas in their praise of quilts. I use 2 Jacks R Better No Sniveller quilts with my Hennessy Hammock, and I'm very happy them. I've slept comfortably on my bed, under my quilt at home all week ( mid to upper 60s°F). I've been comfortable down to 37°F in the hammock. The quilt is my 3 season bag. Douglas has posted a lot of great information about using hammocks in cold weather. Search the forums and your will find his posts, mine and others on this topic. Carol's articles on SUL hammock use should not be missed.