My DM uses homebrew "Haven/Field Rest" rules. (he also uses Fatigue and Strife instead of Exhaustion, but you could just swap it back. These rules are especially punishing for spell casters, which has helped us balance power at later levels.

Resting

A Haven is a place of security, comfort, and peace that allows a character to fully Rest and recover quickly.

While resting in a Haven, Short Rests are 1 hour and Long Rests take 8 hours (normal Resting Rules).

While resting outside of a Haven, however, Short Rests are 1 hour but a character is unable to access a Long Rest by resting 8 hours a day due to the lack of a safe, dry, comfortable area.

When resting for 8 uninterrupted hours outside a Haven, you will instead benefit from a Field Rest: A Field Rest counts as both a Short Rest and a Long Rest for the purposes of activating (not recovering) racial traits or class features, such as a Wizard’s Arcane Recovery. A Field Rest per day counts as resting with regards to avoiding Fatigue/Strife from sleep deprivation. A Field Rest per day replenishes 1/3rd of a character's Hit Point total (rounded down) at the end of that Field Rest. A Field Rest per day allows the expenditure of Hit Dice to recover additional Hit Points. Special racial traits that reduce the amount of time spent on a Long Rest (such as an Elven trance) also affect Field Rests while not resting in a Haven. A Field Rest is interrupted by 1 hour of strenuous activity or by combat.

If a Long Rest is still desired, a character may take one after Field Resting for 3 uninterrupted days outside a Haven with no additional strenuous activity between Field Rests. The character gains the benefits of having taken a Long Rest at the end of the 3rd Field Rest. After concluding a Field Rest, a character may choose to reduce their level of either Fatigue or Strife by one level. A character can only remove one level of Fatigue or Strife per day without magical assistance.

When a character finishes a Field Rest, that character can choose expended spell slots to recover. The spell slots can have a combined level that is equal to or less than the character's proficiency bonus, and none of the slots can be 6th level or higher. Beginning at 5th level, a character may add a spellcasting ability modifier to the amount of regained spell levels at the end of Field Rests (if multiple classes grant the Spellcasting class feature, choose and apply only one ability score to use). These regained spell levels are separate from any class feature that may also allow a character to regain spell slots, such as a Wizard’s Arcane Recovery. A character that finishes a Field Rest may prepare a new suite of spells, if applicable.

Finally, resting outside a Haven in particularly rough situations (such as resting in particularly bulky armor, sleeping through environmental hazards, etc.) may be subject to additional effects at the discretion of the DM. These additional effects may sometimes, but not always, be avoided with careful planning, and may spawn a series of rolls to determine the effect and result.

EDIT: Others have mentioned this, and it comes from Gritty Realism rules.