A lot of people say kobo, but since you are in germany, you might want to consider tolino as well. they use kobo hardware with slightly customized software, and since you don't have to import (kobo does not have a market presence for their devices in Germany), they are cheaper.
I went to tolino from kobo because I lost my kobo and wanted to use onleihe, which is not your use case. but if you are considering kobo, in my experience the devices from tolino are very comparable. loading epub on there is easy and works, no DRM-shenanigans, and wakeup to last-read book on opening a magnet folio as well.
one caveat - while UI is identical, I had a slight dip in life quality (problems opening up specific files, longer loading tines), but I think it's mostly because I downgraded on hardware when I went from kobo libra (like tolino vision) to tolino shine (like kobo clara).
I'm not entirely sure what level of morality you are aiming for... it's an electronic device, and contains lithium and other rare substances which are won and manufactured into parts far away and in highly problematic conditions concerning human rights, as is true for most devices you are likely to own. So maybe not that.
Their cloud as well as online in general is optional for basic use (not updates and onleihe, of course), and their servers are based in Germany, so Datenschutz applies.
You own your files, and nobody asks where you got then from. If you buy from their store or do onleihe, of course there is some amount of tracking. They are linked to German book stores, the one from which you buy the device will be put in as default. However, it's not hard to choose another one from those participating in the program, or buy independently and load the file onto your reader. More details are likely to be found in their terms and conditions.
Yeah, they do not have a device that big. Kobo does, I think, with the Elipsa, but as I said, you'd have to import it and can't use onleihe there, which made it unsuitable for me. Might not be for you.
Tolino used to be a part of Rakuten for some time, all the current devices have virtually the same hardware as kobo devices, with customized kobo software, which is based on linux.
for more details, look here: Wikipedia
I just wanted to say, I've been very happy with both tolino and kobo, the devices last really long, and I want to pull my hair out anytime I have to deal with an amazon device of any kind instead. Take from that what you will!