I posted a similar thread recently and other users gave me some beneficial insights, so I'll sum up what affected my plans the most.
You're balancing your own needs and emotions with those of the people you care about, and you can't know for sure how much it will help them when you're gone, but if you do leave some message behind, it may help them find closure or give them more to remember you by.
Having these final messages left behind or final conversations before also may help give you closure and reduce the guilt and sorriness that you feel about your decision.
As for how to actually leave messages behind, recording some videos rather than leaving a written note may be more personal, clearer, and could give your loved ones something to watch when they miss you. Recording or writing the note in advance so that you can review it to get your words right through a couple revisions would be worth your time imo.
Finally, even if you're not sure if you'll give the message to anyone, writing or recording a message on your reasons and situation may help you reflect on it, and help you either feel surer or may cause you to reconsider your choices.
As for me, I'll most likely be recording a few videos for some of the people most important to me soon, and maybe one general video getting anything off my chest that I feel the need to. I'd make sure they'd be accessible after my attempt goes through, but I may still want to have an actual conversation with one or two of the people I'm leaving. I know not to be obvious about my plans but the only person I'd contact directly is already aware of my intentions.
I hope this helps, and I hope you find a way to escape or overcome your pain.