Hi @plars83 , thank you for your question! Is the Kelty Cosmic 40 that you are using regular or long length? Where is the bag tight? The backpacking bags for 0-30 degrees vary in length as well as their shoulder and hip girth. Determining where you need more room will make all the difference. For example, the REI Magma 30 sleeping bag is warmer and lighter than your current bag and it has an extra inch in the shoulder girth but one less inch in the hip girth. I'd recommend searching for sleeping bags on REI.com and then narrowing your search to backpacking and then comparing your top options - here's a link to get you started! Also, if you live near one of our stores, please come in and try out some different bags to see which option is the most comfortable. I hope this helps. Happy Adventuring!