The first choice you get to make in choosing a sleeping bag is the type of fill: down or synthetic. Down is lighter, more compressible, more durable, and in my opinion more comfortable; but down is slow to dry if it gets saturated wet. Synthetic bags are all the opposites, they are heavier, bulkier, more fragile and will decrease their temperature rating sooner than down; but when wet will dry faster. The other factor is cost; a synthetic bag is less expensive upfront than down, but since down bags live 2-3 times as long as a synthetic, down is more price effective in the long run.
In the last 3-4 years, down manufacturers have figured out how to put a waterproof treatment on down. So, now there is something of the best of both worlds. An example of this would be the Big Agnes Boot Jack 24 sleeping bag. This bag is 2 pounds, 3 ounces; rated at 24 degrees to cover our shoulder seasons or a cold sleeper in summer, and costs $179.99. There is also the Women’s version called the Mirror Lake 22, which weighs 2 pounds, 7 ounces; rated to 22 degrees, and costs $199.99.
Some tips on sleep better can help you extend the temperature range of your sleeping bag further. Wear a hat, insulation layer, and or socks to bed. Fill a water bottle with hot water, slip a sock over, and throw it in your bag to snuggle with. Finally, it takes discipline, but you will sleep better if you go to the bathroom in the wee hours.