i agree w/ what angrysparrow said. just because you got away w/ skimpy hammock supports before, don't mean you always will
& if you land on a rock or a root, or smack an elbow or tail bone, it could set you back more than you'd expect
one place to find the spectra cord is the climbing section at an outfitter. but it's definitely wise to use webbing around the tree... to protect the trees & your fellow hammockers.
and welcome to HF. ...tim