How about using the Amazon built-in collection mechanism? It wasn't present on the Kindle-keyboard (as I recall) so for versions newer than that, I had to start all over. BUT it's been great ever since. The collections live in the cloud, and can be accessed by any (new-enough) kindle. You download whatever parts you want to have local to the kindle.
https://www.amazon.com/gp/help/custo...deId=201733490
You can also organize the collections from amazon.com on "your content and devices".