As I mentioned in my last post, I've been thinking about some of the things I liked about 4th Edition. One of these is the "healing surge" mechanic, which shifts the basic unit of healing per day from the cleric's spell slots to the recipient's ability to recover. The reason I like this is that a party without a cleric (or other dedicated healer) can use their own healing surges to restore Hit Points between encounters, and therefore isn't doomed to "death of a thousand cuts" brutal attrition that they would be in older editions.
To steal this in full would require an extensive re-writing of magic in classic D&D, but there's a "lite" option that's quick and easy. I call this the Health Reserve option.
OPTIONAL RULE: Health Reserve.
Characters get a health reserve (HR) die type equal to their base HD type plus Constitution modifier at level 1. They gain another die (plus Con mod) at each odd level afterwards. Each PC may use health reserve three times per day.
Example: a Fighter with a +1 Constitution modifier has 1d8+1 HR at level 1, 2d8+2 HR at level 3, etc. Health reserve may be used any time the character is free to rest for a few minutes; the dice are rolled and the result heals that many Hit Points. A character who receives magical healing may use HR once in addition to the magical effect, even in combat.
"Behind the curtain" explanation:
Assuming characters get maximum HP at level 1, the HR value therefore restores, on average, roughly half the full HP score. By adding one die every other level, this maintains the approximate average half of full HP. As an aside, characters over name level get "ahead of the curve", but high-level characters have more complex HP restoration issues in my experience anyway.
You might now be wondering: why not simply make HR equal to half the HP total and be done with it, like how 4e's healing surges are worth quarter total HP? A few reasons: that would require re-calculation (with rounding) each level, which is more record-keeping than updating a die code every other level. Also, it would double-dip reward characters who had rolled better for HP by making their healing more potent too; in contrast, the HR die code, like the classic healing spells, gives low-HP characters a larger proportion of their total HP. Finally, making HR a dice roll instead of a fixed value makes it less reliable, and therefore not overshadow healing spells or be too much of a crutch.
Giving three uses per day is based on the nominal "four encounters per day" assumption built into later editions. Having three uses of HR allows for an average of one between each encounter, which will of course NOT be this exact in play because of unequal HP loss, good or bad rolls on HR dice, use of healing spells or potions, etc. Even so, it's useful as a loose benchmark.
As a final note, the addendum allowing healing spells to grant a use of HR keeps even the humble Cure Light Wounds useful at higher levels because it enables in-combat use of HR. This is another way to keep this rule from hurting the cleric's role in the game.