There's one in this thread:
https://www.mobileread.com/forums/showthread.php?t=12872
Though it doesn't do anything you couldn't with a single call to the geometry package.
Is a complete "template" called for here?
Just...
Code:
\usepackage[paper size={90mm, 120mm},left=2mm,right=2mm,top=2mm,bottom=2mm,nohead]{geometry}
and
\sloppy
ought to cover it in most cases. (Using e.g., the book class with oneside and openany options... I saw somewhere that you like memoir, but I've never been that fond of it, but that's fine too.) Tweak the page size (the above is for 6" screen), and margins if you like, e.g., adding enough on the right for marginal notes, or the top or bottom for a header.
As far as readable LaTeX fonts, I guess Computer/Latin Modern is not great for e-Ink screens. I like Charter or New Century Schoobook:
\usepackage[charter]{mathdesign}
or
\usepackage{fouriernc}
I've used kpfonts (Kepler Project Fonts) too.