Could you take BookFusion for a spin and let me know what you think?
BookFusion allows you to upload and manage your eBook collection across Android, iOS and Desktops. All your eBooks, bookmarks, highlights, notes and reading progress are always synced across all devices.
More at https://www.bookfusion.com/reading
Calibre Plugin - https://www.bookfusion.com/reading/calibre
Send to Kindle - https://blog.bookfusion.com/how-to-quickly-easily-transfer-e...
There are a few gaps but a brand new and refreshed platform is being launched in Q3 2020