The easiest way will be to seek for common ctb methods, then modify it. Or create one, there are many things that can kill you. I just read a few weeks ago about a guy that literally decapitated himself by driving against a rope tied to his neck and a tree iirc.
I'm currently arranging a suicide plan that aims to make it look like an accident during a visit to the beach. It combines SN and drowning in the beach.
I'm choosing this because I live in an area where the beach is an hour away, I'm an experienced swimmer, and I had a failed SN ctb so i know what to expect. The beach is also free of dangerous animals and the tide is always high that people often surf here. Drowning is also common here.
The idea is simple, I want the sea to take my dead body so no evidence can be found. I will need to do this during either full moon or new moon when the tide is high. Also need to be done during the night when the wind is flowing toward the ocean (sea breeze). After i watch the beautiful sunset, i'll wait until 7 - 8 PM before swimming as far as I can. Then poison myself in hopes that I will lose consciousness so i can drown peacefully. If not, then I'll just suffer whatever pain SN bring to me while my SI is trying it's best to keep me afloat. I deserved it.
So what problems have I encountered? other than the difficulty of getting my hands on SN again because now my family monitors me, I'm afraid there's still so much I still don't know about the water. This plan is half baked at best, but I still have a month before my time to go.
That's it, perhaps you can try to find a commonly occuring accident in your area and try to replicate it deliberately. For me, it's drowning.
I hope this sparks ideas for you.