As others have written,
there really is no good/reliable/comfortable over-the-counter, pharmaceutical solution (otherwise people would be using/discussing it here already).
Have you considered other methods? Given all your issues (very, VERY sorry for those), perhaps "night-night" (neck compression = same effects as hanging but without the discomfort of having to support the weight of your body by your neck): https://sanctioned-suicide.net/threads/the-night-night-method-mega-thread.6834/ People in pretty physically compromised situations have been able to carry this method out and it requires a only a small set of pretty easily obtainable materials.
I
highly recommend the book mentioned in the Wiki called
Five Last Acts – The Exit Path (2015 edition): The arts and science of rational suicide in the face of unbearable, unrelievable suffering 2nd Edition by Chris Docker. He spends 80 pages on "neck compression" and
it is very well written (the whole book is). Here's the first paragraph:
Compression is a simple method of self-deliverance that relies on no complicated equipment and does not require drugs. The main veins and arteries of the neck are compressed in such a manner that the pressure remains after the person has fainted. Fainting, and death, is a result of lack of oxygenated blood to the brain. It is very quick - fainting occurring within a minute and death following within a few minutes. (In rare cases, death may be accelerated by cardiac arrest after loss of consciousness.) One of the main methods of achieving compression is to use a tourniquet around the neck, carefully positioned so it does not obstruct breathing. Another method is to use continuous looping, and a third is the introduction of mechanical devices [aka a "hookless" ratchet tie-down... those are available ~everywhere... usually used secure a load in the back of a pickup truck, e.g.]. Some momentary discomfort is possible, but brief, and can be minimized with careful forethought.
You quickly faint, while continuing to breathe normally. Death is caused by depriving the brain of oxygenated blood.... My understanding is death from SN ultimately due to ~exactly the same (depriving the brain of oxygen), albeit it takes longer for SN to work.
The hookless ratchet tie-down compression method is my personal backup method. In my careful, brief "testing", the feeling of the strap/tourniquet on my neck gave only minor discomfort. Got one in a drawer 10 feet from me right now. Total cost ~$15.
