Ooo, I think that would be a simple yet effective way to implement difficulty levels.
Easy: As now, save any time and the game autosaves frequently.
Normal: Can save inside your apartment. Game autosaves for significant events.
Hard: Can save only when prompted by the game (at start of day and any other points you think call for it). No/sparse autosaves.
The “easy” difficulty would be accessible for people who want to experience the exploration and story but are struggling with the survival aspects, as well as letting people who’ve played the game before hunt for all the interactions. “Hard” would maximise the strategy (and could be labelled “developer recommended” in the difficulty selection). “Normal” would have a natural curve where at the start you can easily save after each encounter but as you venture further from the apartment you’re incentivised to save less frequently.
You could include other tweaks like weapons not breaking on “easy”, but I feel like changing the rules for saving would do enough on its own.