Running 4.2.8283 firmware? Due to a framebuffer change in this firmware, anything older than January 2017 probably won't work. Try this one.
https://github.com/gtalusan/kobo-nig...r/KoboRoot.tgz
Have you tried AMOLED displays yet? It's the next best thing after eink, no backlight, black is black and white text you can make shine as brightly as you like...