Something I suggested before (and which was kinda widely hated lmao) was that companions show some disapproval if you attempt to long rest too frequently. Lae'zel urgently wants to reach the Creche before she turns into a mind flayer; why would she be perfectly content with the party taking a long rest every hour? This is a compromise, where you are disincentivized to long rest too frequently, but not restricted from doing so. Another suggestion I've heard is that companions gain a level of exhaustion at some point, and until at least one companion gets this condition you're unable to rest because the party isn't tired enough.
But of course, determining the threshold for this disapproval or exhaustion is the big question, as is for every possible long rest system. Do you get a long rest opportunity at specific story-beats? At every X, Larian-determined "important events/locations"? Base it on total hp lost of the party - if so how much? At certain locations on the map? Pros and cons to each.
I enjoy this at a glance, not particularly expensive to implement either.