Numerical bonuses? What are those?
The basic idea is that every attack deals 1 damage, as do most environmental hazards (some deal a bit more).
However, you have 1 ICHP (In-Combat Hit Point) and ~3 OCHP (Out of combat HP).
Effects that let you survive attacks in combat either give you about 1 extra HP, or let you treat an attack as an environmental effect, thus sending it to your OCHP.
I envision a "holy crap, he's tough" combat character having 3 ICHP, and maybe 4 OCHP, as well as effects that let you treat attacks as environmental effects (there might even be enemies that only have an environmental HP pool, as a way of representing really large creatures; the attack has to essentially be equivalent to them falling into a pool of acid for it to work.)