Just buy an old Kindle for $15, register it, and put it in a box and forget about it.
Then buy your ebook and download it to your computer (selecting that Kindle), and then put the file in calibre and convert like you're crazy (if that is your predilection).
I have, use, and love both Kindles and Kobos - and so I have no problem whatsoever with what I want to buy, where I want to buy, and what I want to read on whatever device I own.