Man, if I can't figure out a few pieces of seatbelt and some rope, I don't deserve to be in mechanical engineering anyways.
People on here are going to definitely tell you that your life or the ability to walk is not worth experimenting with a DIY saddle. Having said that, plenty of people do use DIY saddles. My first one was cobbled together from an old safety harness and 2” triglides.
If you decide to DIY, test the heck out of it at ground level.