>>314139772
Definitely one of the more easily attainable methods along with some bonus points for, uh, "gracefulness" of it.
However, my worries about this come from some recent research about failed cases which turns the person into a vegetable. Not sure how they ended up to that point though. Getting found too early? Masks not secured well enough? It seems to me that those shouldn't be a problem with some planning beforehand. If I recall correctly there was some talk about another gas being an even better option instead of helium, can't remember of the top of my head.
Still, this method is one of most preferable ones, if it is reliable as they make it out to be. I think this and hanging would be my preferred choices (excluding firearms as I do not have access to them)