Do you have any recent backups of your My Documents (or ~/documents on Mac) folder?
Maybe a Windows shadow copy? Right click a quick/auto save folder in Windows Explorer and select 'Restore previous versions', if available (or right click, Properties, Previous Versions tab).
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin\PlayerProfiles\<ProfileName>\Savegames' folder.
You can increase the number of quicksaves and autosaves kept in the Game options (up to 25), which will reduce the chance of overwriting your most recent saves if you try a new game for some reason and forget to switch to a different profile.
Periodic named saves are always a good idea. Saves are fairly compressible, especially if you have a bunch of saves and use something like
7-Zip's .7z archive format.