NEVER, EVER force an autosave to overwrite a manual save. Lost all my progress because I created a new game to try and see the Leave Jewel scene. When you autosave, if there is no current autosave, create a new file. If there is only a manual save file, DO NOT OVERWRITE IT. NEVER OVERWRITE A MANUAL SAVE FILE WITH AN AUTOSAVE.
Autosaves always save to the 'Autosave.sav' savefile. They don't save to any manual save you create separately from the 'Autosave.sav' file. We'll look into changing how autosaves work to prevent progress being lost if you don't create your own save file separate from the autosave.