[hobnail]

What Pajamaman said. With calibre the Kobos handle collections beautifully. They also handle series, separately. (It used to be that series were organized as collections but that's no longer necessary now that Kobos handle series natively.)

Of course, if your books are in kindle format, but that's not a problem since calibre can convert them into the format the Kobo wants, epub.

I buy my books from Amazon, download them from their My Content and Devices web page, then load them into Calibre. The Apprentice Alf plugin removes the DRM so then I can convert them to epub.