Ask HN: How do you organize your iBooks collection?

I am looking for tips on overcoming the burden of an overgrown iBooks collections. I find most painful the lack of a global search within the app, as well as the inability to add a book to multiple categories/collections.

Any good way to bring some organization into this mess? For now, my only other way of storing my books is as a backup on Google Drive, but the syncing is not as seamless as with iBooks, so it is still my preferred option.