Calibre is what you need. With Calibre you can create an ebook library on your PC, and can catalogue your books. Yes Amazon has your purchases backed up, and they also have any books you've emailed to your Amazon account. What Amazon won't have is any books you sideloaded vis USB direct to your kindle.
Don't you have your non Amazon ebooks on your PC? If you don't you should really think about backing up your non Amazon purchases at least.
https://calibre-ebook.com
Any new kindle you get will have access to all Amazon and Send to Kindle ebooks once you have registered it to your Amazon account. You don't have to get rid of your Paperwhite, you can have multiple kindles registered to your account.