I have a double, and when you see people completely enveloped in their hammock they may be hanging incorrectly. If you lay on a slight diagonal, you can lay flat as a pancake.
If youre looking at saving a few bucks, go for the single. however, if you think you may want to use it more in the future, spring the extra few bucks and go double.
Either way, I think you'll be happy, an early congrats to you on your purchase, whatever that may be.