I used to think, there must be a better tramp material, until I built a couple.

The best tramp material, for performance, I have seen is knitted polyester and looks like lace (see Sailrite, tramp material). It has big holes, it's light, and soft on the knees. The untreated version is good for 1 maybe 2 years, in the sun. The UV resistant version is good for 4-5 years, best guess. When this stuff fails, it fails fast. You go from, "I really should do something about this" to falling through into the water in a couple of weeks. I was lucky, mine failed while working on my boat. Friends tell me, it really sucks to sail home with no tramp.

The very best woven polypropylene tramp material works almost as well, is a little heavier, a little cheaper, and lasts 15-20 years in the sun. You can expect to re-stitch a tramp 1-3 times before the material breaks down.

Polypropylene net, you have already discussed.

Now, if you to try something new, once I saw a H16 whose tramp had been replaced with aluminum grating. The workmanship on that boat was way way below sh*ty but it had some advantages. If you could just solve the problem of it being a giant cheese grater, you are going to slide across.