Using items is a bad idea, they don't get removed after use and leak.
Instead use "+HP bug". The ability that permanently increases hero HP ("Item hero health bonus" or something like that) only modifies HP on add/remove, not when it changes level. So you can make such ability that adds +11 HP on first level, +1 on second and then add it (hero gets +11HP), set it to level 2 (no change) and remove it (hero loses 1 HP).
That way you can increase HP permanently (also works for the according mana bonus ability)
As I said, create an ability based on "Item Life bonus" with two levels, first level adds X+1 HP, second level 1 HP. Then, in the trigger, just:
1. Add this ability
2. Set it to level 2
3. Remove it
It will leave the hero with X bonus health.