Band of Regeneration

The healing here runs on its own clock. Normal regeneration slows to nothing while you are moving or taking hits, which is exactly when you need it, and this ignores all of that. It ticks at the same speed whether you are standing in a house or kiting a boss around an arena.

It also survives Bleeding. That debuff shuts down your natural recovery and leaves this ring untouched, so it is one of the few real answers to an effect that otherwise just makes you drink potions faster.

Casters want three. Two become mana regeneration bands, and one of those feeds the Celestial Cuffs, which stay in a mage loadout for most of the game. Gold chests underground and the chests grown inside living mahogany trees are both worth opening with that plan in mind.