The simple solution is to stop buying eBooks from Amazon. Pirate all of your epubs and PDFs so you will always have an offline backup. If you enjoyed the book buy a hard copy for a friend, relative, book club, etc from a local book store. Amazon doesn't need your money anymore.
Your solution hurts authors more than Amazon. Just buy ebooks from somewhere else! Don’t be cheap and pretend it’s principled. I know you say buy a copy if you enjoyed it but that’s not really how commerce works and none of these authors agreed to offer you donationware.
I'm all for also buying books, but my local library has all the books too, so it is sort of how the commerce of books works (at least where I live).
Also if people are still buying ebooks or kindles from Amazon after the whole 1984 fiasco I doubt they're going to care about downloads.