Right to die organizations recommend helium and end bags due to their reliable painlessness and accessibility (helium can be bought, end bags bought or DIYd).
If you wanna try any other methods, thoroughly research their painlessness and safety, including from peer reviewed (medical) research. A lifetime of exposure to tv and a culture that's been formed by and values survival have taught us overestimates of danger and efficiency - as a result, most attempts fail and many/most successes are unnecessarily painful. Overdoses are very ineffective and even gunshots to the head aren't instant or successful 100% of the time.
As the letter in
https://sanctioned-suicide.net/thre...or-guests-lurkers-and-curious-parties.103638/ and reports of people surviving absurdly high falls show, a high place is definitely a risky one - to avoid.
Regardless of method, research how to do it right, how to approach it best. I'm not sure but I think preventing "too injured to try again" may apply to the helium and bag approach too - that if there's a failure far enough into the process it can result in brain damage (but I don't know detailed instructions so I can't personally say if it's really possible. Best to err on the safe side, so - research.)
Don't be discouraged by my safety speech btw - death is universal, after all, and choosing a safe method and doing it well is great.
I wish you well, man!