Undrave
Legend
That sort of hp/resolve/stamina split worked well in starfinder, it's a shame that it would be such a headache to convert 5e to similar
How I’d do it is:
Everybody got Stamina, everybody got HP. Whenever you’re hit you can spend Stamina to improve your AC, basically being you exerting yourself to get out of the way or deflect an attack. Say, +5 AC per Stamina spent. If you don’t, you get hit and take HP damage (in this system HP would be smaller numbers than what we’re used to, but so would the damage you take). You can recover Stamina on a short rest, up to half your daily max (or more with a Bard or some Inspiring figure in your party), or fully during a long rest, but HP takes longer without special care (like 1 HP per long rest, maybe 2 with some mundane healing stuff or potions, more with expensive rituals).
Beyond the basic, the Fighter types could spend Stamina to improve their weapon attacks in some way (more damage, knockback effects, etc). For Spellcaster, whenever you cast a spell you have to make a check or lose stamina in the process, with the strength of the spell determining how much stamina you lose (Cantrips wouldn’t drain any), and some even only letting you take half stamina drain if you succeed. Concentration would also be rolled into Stamina. On your turn you can either spend your whole turn concentrating to maintain your spell, or spend stamina to be able to do something else at the same time.
That way everybody's got a similar resource but they interact in different ways and casting powerful spells would be risky and exciting.
In this kind of system I'd probably create rituals that would be exclusively rituals though.