ThrorII
Adventurer
Having class abilities tied to a 24 hour clock. "Once per day you can sleep 6-8 hours to reset class abilities".You could just make long rest abilities reset once per day. It's functionally more or less the same, but decouples it from resting.
Short rest abilities you could say recovers every 3 hours roughly (whatever time interval you choose)
Tie rests and healing to the old B/X mechanic: "Every hour you MUST take a short rest of 10 minutes. Doing so allows you to spend HD to replace lost hit points". Make HD replenish every long rest, not hit points. If the short rest is forgone, the PC earns 1 level of exhaustion.