Adventures in mapmaking: the search for grayscale tiles
newsletter.pnote.eu
newsletter.pnote.eu
This would also let you set the grayscale on the tiles using imagemagick convert.
Neat project and thanks for the write up.
Instructions for self-hosting a PMTiles file are available here: https://docs.protomaps.com/.
Another option would be self hosting vector tiles(or finding the most generous free tier vector tiles) and using a custom grey scale styling that you could tweak to your needs.
Maputnik is a great tool for building custom vector stylesheets. (1)