Unfortunately quick, quiet, and not requiring preparation is a complete unicorn. Due to how hard the quick/quiet/peaceful ways are to acquire the parts for, there's a lot of prep that has to go into it.
I would discourage taking a knife to yourself as exsanguination is incredibly painful and the SI kicks in BIG TIME with that much pain, making it a lot more likely that you will just end up hurting yourself/possibly starving your brain of blood enough to cause brain damage but not death.
Something like SN would be the closest to quick/quiet, however it will need prep. N if you could get it would be even better, however getting it is nigh on impossible in the west especially.
Good luck, I hope you find what you are looking for