JEB
Legend
So if I'm reading that correctly, you'd get twice as much healing in a combat as my troll build, or the Dwarven Fortitude feat, grants. Plus it recharges enough on short rests to give you at least one more heal in a subsequent combat (more if you didn't use your entire 2x level supply the first time). That's pretty generous! But if it works for your games, that's great.Maybe like this:
You have double the number of HDs as normal per your level.
you regain all HDs on long rest.
you regain 1 HD on short rest. 2 HD at 5th level, 3 HD at 11th level, 4 HD at 17th level.
You can use your Action to spend a HD. 2 HD at 5th level, 3 at 11th, 4 at 17th.
You cannot do this again until 1d6 rounds have passed or you suffered Acid of Fire damage in this or last round.