The emotional regulation part looks promising to me. How does that kind of journaling look like to help with that?
I never sent one of those letters. The writing alone made me feel so much better or gave me a resolve to act that the letter would have been outdated by the point I sent it.
However, some prefer longform, written or typed, different apps and such.
What I found helped me was trying to focus more on how I was feeling and less on what was happening, as I think it's easy for me to rationalize and become more and more distant from how I'm feeling. Darn, now I want to revamp the app.
[0]: www.ifeelio.com