Coleman - Kompact 30°F Rectangle

Camped when it hit 28 overnight. We put moving blankets(2 under and 2 on top)the air mattress, I used a Coleman sleeping bag that was rated for 30 degrees. Wore thick socks and a sock/slipper thing on top, thermal/base layer, hoodie, beanie, thermal leggings, left sweats in my bag if I needed them, 2 blankets on top of of me. Tossed a large hot hands into my bag and kept the other in my hoodie pocket. Slept great. Biggest learning curve is you instinctively want to zip your tent up tight, but you need the ventilation to keep condensation from forming and getting wet. We ran a small fan and zipped our window down about 4 inches

I agree this is the way. Two bags. Originally bought a bag rated for -10c but woke up shivering in the middle of the night of -6c. Now I use a Coleman rectangular bag over my -6c down bag. Makes a world of difference. Plus that with the double bag system you can use just the one in more warmer temps.

Most rectangular Coleman sleeping bags can be zipped together and won't break the bank.