Aside: what's the best e-reader device (ignoring cost)? I'd like to invest in one soon, something robust and durable, good contrast. I kinda like the idea of running open source software on an ereader but I'd probably consider it merely nice-to-have.
Kobo is more open and is price competitively with Kindle. It's also much more customizable if you are into that.
There are also a lot of Android e-ink tablet like BOOX. These are more expensive but a much, much more customizable as it's basically an Android reader.
Contrast shouldn't be a problem with any recent device. But anything release in past 1-2 years are excellent.