Omg thank you for telling me. I thought it was easy as 1,2,3. What if I'm assured by the seller it really is 100% helium?
See if you can download a product data sheet. I've found some in the UK which is sold as 100% and the data sheet confirms it's 99.99% He.
Arguably Nitrogen or Argon are easier for the home consumer to purchase though for brewing or welding. Also, He has the bad rep for exit bags hence some suppliers regulating it to trade only.
Remember too that whilst all three are inert and would do the job, we breath 78% nitrogen permanently and it may be more natural and comfortable - my only personal experience of helium is squeaky voice from a party balloon.
The setup sounds far more complicated than it is. Read the megathread and ask any questions. Flow meter regulators and bags are available from Amazon as is hose. You need an Argon flow regulator that you can set for 21lpm (that's the conversion to use an Argon flow meter for 15lpm Nitrogen).
If you're in the US or the UK nitrogen/helium/argon all have the same thread. I believe some countries may have varying cylinder fittings.
I'm sorry you find yourself in this place, sometimes it helps just discussing an exit. I've had these thought for decades but I'm still here. Many members have even procured their full exit requisites and take solace just knowing they can CTB if they want to. The suicidal mind is complex and we're all different in how we function (or not).
Seriously though, check the inert gas mega thread, it's a mine of information.
Exit Bag and Inert Gas Basics —A very, very long post, I know, but I feel like I've fielded a lot of questions about this, so I figured I'd spell out everything I know. Others on the forum should please add to this thread whatever reliable technical information they feel is appropriate for...
sanctioned-suicide.net