DnD Homebrew

I am trying to translate the Fiery Faith passive from Vermintide 2 for a players Barbarian Zealot. As the passive states it should be a high risk high reward kind of thing.

The most simple 1-on-1 conversion imo would be:

"For each 1/4th (rounded down) missing from your max health you gain a +1 bonus to attacks."

Which sounds the most fitting and true to it's original intent, but it might be a tad too strong. Maybe a more hardset table of tresholds would be better; something like "at 30 health gain +1 to hit, at 15 health gain +2 to hit and at 5 health gain +1 to damage and +2 to hit".

Two other ideas came to mind:

• As a bonus action, deal yourself 'x' damage to get a bonus on your next attack.
• When getting attacked, forego your AC and take the hit. Take a dice closest to the amount of damage you took (rounded down) and add it to your next attack as bonus damage.

These could work in their own way, but I feel that they don't really hit the high risk high reward side that the original passive has: keeping your health as low as possible to deal as much as possible damage.

What do you guys think? Any advice to get it as close to the original passive but keeping it balanced? Or maybe a different idea? Would love to hear your thoughts!

P.s.: typed on phone, please excuse any typos!