I think a fairly good compromise would be to introduce a PoE2 system with some modifications.
In PoE2, the spell slots automatically returned after the fight was over, while rest was needed for healing and also gave some bonuses.
One could try to introduce this system by making the classes based on a short rest regain their slots when the fight is over.
Characters based on a long rest to recover any slots normally.
While resting, you can use food that gives you various bonuses, the more powerful the rarer, of course.
When you rest again, you lose the bonus, which would encourage you not to rest (provided that it is powerful enough)).
The food itself could even be an optional item in such a situation.