My cowboy camping is always with a basic bivy. I simply want to be able to zip up and be separated from bugs, or rain, or other forms of creepy-crawlies if needed. I am not fond of rodents inside my sleeping bag. My bivy weighs 1# 4-6 oz (I have three to choose from).
I love the way you can see the stars when in a bivy! On short trips (2-3 days) I really prefer this. Depends on my goals, but sometimes comfort at night is NOT my main objective.