@weamish - I am currently using a Calibre plug-in created by some GREAT folks that allow Calibre users to now manage Collections directly within Calibre.
Calibre has now become a one stop shop for ALL my ebook management and I just can't thank all the folks over in the Calibre forum for this terrific plug-in. By the way, that's just one plug-in, there are a bunch available to make managing your Library much easier. The Kindle Collections plug-in is just one. You might want to go to this link and check it out:
https://www.mobileread.com/forums/sho...d.php?t=118764
Piece of advice: DON'T BE AFRAID TO ASK QUESTIONS, if you don't understand how something works. I needed a little help configuring the plug-in (and I am SO NOT a programmer/developer) but every question I asked I got a straight, easy to understand answer. You have nothing to lose and Good Luck!
See below for a screenshot of how my Collections are organized - this was all done with Calibre.