You have a few options.

If you want to save money, a Kobo or Kindle is a good starting point. Obviously tracking and logging pre-installed so keep that in mind. But there are ways around the DRM locks, and Kobo can be moodified to run KOReader.

If you don’t want the slow and laggy e-reader experience, any Android tablet will do so long as its not those “cheap” ones you find at Walmart. With the exception of the Fire Tablets (they are subsidies), you’ll probably want to spend about $150+ on it. A used tablet with Android 8 or newer should work too. KOReader again is available and is the most compatible e-reader app, with Moon Reader as my fallback.

But if Money is no Object, you might as well get an iPad, the pre-installed Book app from Apple is amazing, easy to use, and if you disable iCloud for it (unless that’s what you want) versatile. The best bit is, you can even use an iPad Air 1 and it works well. Sure transferring books is a pain, but it can be done with iTunes.

However if you want eInk, then you only option is an Android e-reader. Onyx Boox, Pocket Book, Bouye, etc. The problem with these devices is that they are not cheap, and they will get dropped before an update becomes available. I have experience with Boyue and Onyx Boox. My two Likebooks, are stuck on androids 4.4 and 5, and never had an update since I got them. While my Onyx Boox has surprised me and had an update this week for the baked in apps though the OS version is still 10.

In my view I think you need to get a good but cheap device, old iPad, kindle, etc. Use it and break it. Find what you do and don’t like about it, then spend good money for the box that fixes it. I started with my Android tablet and hated the battery life, my Kobo sucked because it has no color. I got a Nova 3 Color and I’ve been quite happy, but I do miss the MicroSD card.