I'm sorry you're having such a difficult time. Although I don't know your situation, I can sympathize with your fears. I've failed ODing, night-night, and partial hanging (multiple times) so I can relate to how much it sucks to back out of it. I think what helps most with accepting the decision to CTB, is to set a clear date. If you constantly think "I'll just do it when I can't handle this anymore" then it's a lot easier to let the fear overwhelm you and push it back. Having a set date sort of helps with the anxiety surrounding the decision, because I could let out my anxiety over time as the date approaches, instead of letting it overwhelm myself on the spontaneous date I decided to attempt.
If you're concerned about whether or not the SN is good, the blood test is the best way to test your SN. You can search for "blood test" and find a bunch of threads with helpful information.
In terms of comfortableness... that's up for debate. I can say from having experience with both, that it was significantly easier for me to mix a drink that I thought would take my life, than it was to tie a rope around my neck. Plus, I take solace in knowing that even if I screw up my SN attempt, I probably won't have any lasting effects. I have several mental side effects from failing OD, and the thought of waking up crippled from failing hanging was what made me stand up multiple times. But if you fail SN, then you probably won't have any lasting side effects other than the usual disappointment and shame that follows a failed suicide attempt.
You'll probably experience extremely rapid heart rate and a bit of difficulty breathing, but I think those are a lot more comfortable than the thought of crippling myself by failing with other methods. From failing OD, I can say that vomiting repeatedly definitely doesn't feel amazing, but like, most of us have vomited at some point in our lives, so you probably already know what to expect there. I take a bit of comfort in knowing that if even I experience these things during my attempt, then at least it will be the last bit of pain I have to feel before leaving this world.
I'm sorry again that it's a particularly difficult time for you. I hope that whatever decisions you make can lead you to the peace you deserve. ^^