So Plan B for me is SWB. I will use Alcohol(wiskey) to suppress my SI. I don't think there is more that you could do, since you need quite some strengh to hyperventilate for 10 minutes straight(so no sleeping pill that make you fall unconscious faster) .
If I fail on the bathtub I might go out to a lake and swim(hyperventilate on shore, jump in, hold breath) so I can "distract" my SI by diving around.
This is a really good idea.
Heres a little anecdote copy paste from a reply i made to another SWB forum post about my own experience that backs up your ideas:
unless you are 100% certain and determined, you will most certainly cancel your plan. You will be hyperventilating and then you will feel numbness. Either you will cancel or be more determined. How do I know? I started recording myself to leave behind. Yes a huge amount of appeal to this method is that it looks like an accident, however, I was doing this in a bathtub. I WAS going to be found and for my life situation it would have been best to leave SOMETHING. I was watching myself, honest to God, thinking about how it was some of my last moments and what people would see. Why did I turn back? The bathtub wasn't filled enough yet and the numbness in my toes was scary and the possibility of failure felt too high. I have never had a real near death experience, so maybe those who have overdosed or died and been resuscitated will have no fear or consider turning back. I have never faced a failed attempt and never want to. I was institutionalized weeks ago because I blabber mouthed about how I was getting a shotgun, because I couldn't have just let myself figure it out myself whether or not I wanted to CTB. Now I have no method that can just be done without risk of survival. I don't have any poisons or the willpower to hang myself. I cannot do any of it because I refuse to be institutionalized again and i refuse to live severely impaired with a higher difficulty CTBing. After i changed my mind I went and took a shot of liquor. I have been writing this all after that moment.
TLDR: Have a really really good reason to CTB if you're using this method or any other method where you are capable of turning back. Be truly strong and truly suicidal.