My current pack is a Gossamer Gear G4. This weekend I was expecting temps in the low 40s, so I put in a Walmart blue pad and the black intermediate bag from a surplus MSS sleep system. That setup kept me reasonably warm, but it took up almost all the room in my pack. I have wanted to get a down top and bottom quilt to relieve some of the space issues, but that seems to be about a $400-$500 outlay.
It rarely gets colder than 20 degrees here so I can make do with 3 seasons, but I also have to deal with summers where one can be dripping with sweat when you get into the hammock but still wake up in the night with cold butt syndrome. An underquilt which can be moved to the side seems ok (I actually own two poncho liners, so maybe this is my summer option), but getting a summer weight under quilt is also pretty pricey.
What is the best course of action for me here?