First of all, sorry to hear about your failed attempts. It's a very disappointing feeling to say the least. Failed a bunch of times with partial suspension. And failed a short drop, which ended up turning into a partial suspension hanging, since I ended up with my toes on the floor. And failed the partial suspensions because I couldn't pass out since I couldn't get enough pressure on the carotid arteries. But it's taught me a couple of things for upcoming full suspension hanging.
1. Even though softer around the neck does feel better. Towel/Scarf. A rope is better at putting more pressure, and centralizing better where you want to put that pressure. The softer, the larger the distribution of pressure. And as far as rope goes, static climbing rope would be better than cotton, since the cotton ropes have more stretch than you might imagine.
2. Thickness is important, too thin, and you'll feel it cutting into you. And something way too thick isn't going to localize pressure as well. Most people here suggest static climbing rope between 12-16 mm. And those seem to be the most popular widths when searching online. But I've een seen some up 20 mm, which I believe they said it was rope for gym climbing.
3. In partial suspension hanging, a lot more chance of survival instinct interrupting the process. Full suspension, is more of a done deal.
4. Weed might make you feel a bit too paranoid.
5. Alcohol makes for great liquid courage but makes for sloppy work when you're too intoxicated. If getting massively drunk, now I would have to check, and recheck, verify, test, multiple times, before getting drunk.
6. Pretightening noose around the neck is really important. As well as having the least amount of slack possible. And the shorter the drop the better, less yanking, and less changing of the position of the noose around your neck.
It's not my information and it's all been said on here before. But it's crazy how sometimes we miss little things by accident while reading through it all. Plus, we're all slightly different anyways.
Best of luck. And (hang) in there. Ha.