I've fallen asleep in a hammock hung by 550 cord, woke up still above the ground. (Regretfully, I'm a little more than the 150 target weight you have in mind... so that's good news, you have an extra margin of safety!)

Both ends were doubled, and went to straps that go around the tree. This was real 550 cord. There are plenty of cheap imitations that I wouldn't want to use to support a human... Also, the static capacity wouldn't be an issue, with even one line, but, the shock capacity if you, ah, dropped into the hammock might be an issue, especially if you had any abrasion. The straps around the tree seem to help.