I'd consider using a 7" to 8" real Android tablet for this. If using primarily as an ebook reader replacement, but want something that can also run basic Android apps like Feedly that won't overtax the CPU, this would be a reasonable approach.
Here are a few good Android tablet options in your size range, at various price points.
1. Huawei MediaPad M5 8.4. Excellent specs and premium hardware. Keep your eyes open on Amazon and other places, price fluctuates between $289 and $319 recently.
2. To save a few $ but still get a quality high res screen, consider buying an older existing Android model and just updating the OS version with a custom ROM. CPU won't be quite as fast, but these are perfectly usable and Feedly runs great on mine. Three good options for this are the Google Nexus 7 2013, the Asus Zenpad 8, and the Samsung Galaxy S2 8" from 2016. You can still find any of these for new on Amazon or other places. For an example on how to update a Nexus 7, see my post
here on how I did it.
3. A forthcoming new Samsung 8" tablet that looks interesting, good specs, is
here. Catch with this one is I don't know exactly when they'll release it or price point.
4. Also, there are of course a plethora of other less expensive Android tablets. Samsung has a current model Galaxy Tab 8" that runs around $200, it's just lower resolution. At the lowest price point, Amazon has a Kindle Fire that's 8" and gets good ratings.