I see a lot of people recommending removing the DRM, honestly, if you bought the book in Amazon (or Kobo or Barnes & Noble) I don't see an ethical issue with sailing the high seas to get a DRM-free version of it that you can properly backup and read anywhere.
you'd have to take the DRM out of the books, convert them to epubs and then transfer them.
its an involved process but that's always going to be that way on any e-reader that's not a kindle (or android based, where you can install the kindle app).