Different rest restrictions on different difficulty levels are a bad idea. How then to design these fights? What level should be the default? Is this location possible to clean in all systems?
In this case, it is not enough to weaken or strengthen the opponents for each encounter. In this case, you have to design all battles separately for each difficulty level.
In most games, when you change the difficulty level, the strength and possibly tactics of the enemies usually change. Their quantity or type is almost never adjusted.

The game itself is clearly not designed for very limited rest. I am not sure if trying to include it at this point really makes sense, it could cause more problems than it's worth.
It is better to design fights so that they use as many resources as possible than try to force the systems into which the game was not designed. As a rule, it doesn't end well without a major overhaul of the game.