I have found out the hard way that you need a lot of overengineering in your rigging.
Line tension is related to the ratio of the length of the line, the amount of weight, the sag and the distance between the two trees. I won't go into the math, but suffice it to say that as you tighten the line so that sag becomes nil, the tension tends to infinity. What that means in practical terms is that the line tension can be many many times your weight.
I buy Spectrafiber from a sailing chandler. They only sell 3 kinds of cord: nylon for low-load applications, Marlowbraid (all polyester) for medium load and spectra for high-load, high performance control lines where there is a need for low bulk, low weight, low creep and good wear characteristics.
High quality/ high-performance paracord has a breaking strain of 250kg (550lbs), whereas 3mm spectra fibre has a breaking strain of over a tonne. But the big difference is in creep. A single strand of paracord as a suspension line under my weight of 165lbs may elongate by 20-30%. That means I set up and slowly it sags more and more till in the middle of the night I'm on my arse.
By comparison, Spectrafiber's (or Dyneema's) creep is negligable for these purposes and timespans. It's what you want and worth the effort to find. Trust us.