I believe, it's not a bad idea to combine this method with CO.
To overcome the SI is a matter of emotionsless practice and to have deep peace and the warming wish to go to the other side in that moment. For me I would think about the reunion with my beloved wife. I lost her 2 years ago. Because of several terminal illnesses, there was no chance for her. I rescued her from the Dr. Frankenstein like hospital and brought her home to our poodles. She passed away two weeks later, holding my hands, without any pain or fear.
Convulsions can be a so hard with Nitrogen, that I need a very strong chair with armrests, and the chair must be fixed at all 4 legs, and the upper body has to be taped around the chair.
If anything goes wrong, I can have a brain damage already after 3 or 5 minutes.
Surviving CO you can also have brain damages, but they come delayed, days or weeks later. In Germany there are some cases, where people survived CO. They have been in the news, because it have been crimes. In one case a mother tried to kill her kids with CO together with herself. The kids died. She survived. She appeared months later before court still only with a rollator due to the brain damages.
So, Nitrogen or CO, in both cases you face the risk of brain damages.
The difference with CO is, if the CO level is high enough, the SI has no chance anymore, because I am unable to move. Even if SI says, I shall leave the room, I can't. And moving out of the room is the only chance to survive with CO.
CO is really not that painless. There are many side-effects like very strong headache, neusea, vomitting, chest pain and convulsions, also the risk of amputations, if you survive, but with enough charcoal in a small toilett it's nearly impossible to survive, with the right concept. Not everyone is facing that side effects or all of them.
If the bag or helmet or whatsoever does not work as it should be with the Nitrogen, but at the same time I have also CO running, then even if something goes wrong with Nitrogen, there is still the CO in the room.
If I am already unconscious due to Nitrogen and then something unexpected happens, probably side effects of CO will show no impact. The CO will just end it while I am sleeping.
The set up is more complicated. Tubes and the bag must be heat resistant, the Nitrogen bottle for the same reason outside of the toilet, connected with the tube through a later sealed hole in the door.
SN is no option for a combination with Nitrogen for me, because vomitting into a bag or helmet can lead to aspiration of it.
SN kills me only after many hours, CO within 1-3 hours and Nitrogen within one hour.
Many say, 40 minutes are the failsafe maximum with Nitrogen, I say, Gaussian bell curve is the evidence, that there are people, who will survive longer and die earlier under the same conditions. If there are small leaks for O2, the whole process lasting longer.
With a 10 L bottle (uncompressed 2,000 L) and a minimum flow rate in my opinion of 20 L/min, there is gas for 100 minutes.
I will never use gas for less than 60 minutes and a flow rate of minimum 20 L/min.
Don't forget: If one will use Nitrogen, the #1 rule is to avoid surviving with a brain damage. This can be almost ensured by the other brain killer, CO, which will also neutralizes the remaining SI.
The Scuba option is no option for me, because even with this expensive masks it's very difficult to get an airtight seal on the face. And when the convulsions begin and the face muscles change their behavior, it could be a failure.
Any mask is a risk.
A helmet with an one-way-valve could be the perfect replacement for the exit bag. It would also be a working option together with CO to resist the heat in the room.
Sedatives are a must for CO. But my plan is not to pass away by CO but by Nitrogen. CO is the failsafe. I can take the sedatives moments before inhaling the gas.
If I would have a gun, my method would be Nitrogen and seconds, after the bag or helmet is on my head, a shot into the heart on 31. December, when everywhere is firework.