If you have not too many books, it would make sense to make two collections, Read/Unread. Than you'll know always where you are. (metaphorically speaking).
For example; _ A. Read and _ B. Unread
Make sure to have a space after the symbol _ ( or any other).
When you let your books( on the Kindle) show by 'title', on your home-screen it gives you the two collections first, sorted by alphabet ( _ A. _ B. )
When you've bought/uploaded books, you let your books show by ' collections' ; that gives you the collections first and then the books you've bought/downloaded on the Kindle.
If you really want to get into sorting and collections, you could look for the Windows Collection Manager or search by ' collections' on the forum.
There's lots of people that have some good ideas about it.
Good luck.
