Wow this is brilliant, and I can't believe this wasn't obvious to me when I've considered voice typing but felt weird about it.
I just got a Note 9 and I love that I can pull out the pen while the screen's off, jot a note and put the pen away without having to unlock my phone. And in the app it can be OCR'd for searching, editing etc. I'm sure once I get into the habit of using this I'll be forgetting ideas less.