I've been using a 11 foot length of 550 Paracord on my DN. I just tied a small loop with a bowline knot at the head end and an adjustable loop with a rolling hitch at the foot end. I've replaced the stock rope & carabiner with a amsteel continuous loop & SMC ring and my ridgeline runs between the rings. I currently have the length set at about 96 inches (83% distance between rings). The paracord was just a cheap solution for me, picked up 100' for $8, but it is a little bulky and does have some stretch to it.
I just got a spool of Lash-It 2.2mm last week and have upgraded my ridgeline to that. 1.75mm is rated at 500 lbs and 2.2mm is rated at 650 lbs. I weigh 230 and either would have worked. Keep in mind, the force on your ridgeline is much less than on your suspension, if you hang at the proper 30* angle. If you don't want to buy a whole spool like I did, you can buy it from Dutch's site
in 25 foot lengths for pretty cheap and it's not that hard to splice yourself.