I was using a north face cats meow and got cold at 30 degrees, my choices are try a sea to summit reactor in existing bag or upgrade bag. Has anyone tried the reactor? Or, looking at a Big Agnes Mystic Sl, no insulation on the under side of bag, would use this with neoair xlite. Any thoughts? I'm open to other bags also, the Mstic is large and lite. How do the bags with no underside insulation rate with users?