1) You should always enhance Novus so new rules are optional. So I would keep hit points just as is and called hit points. You can "re-skin" them via description (hit points represent your ability to avoid being hit and stay up in combat and stressful situations...).
2) I think you should enhance the existing boon point options for Combat Boons. These would function exactly like a "critical" (Boons are basically a critical, yes?). There should be options based on the number of Boon Points spent.
Example;
Lasting Wounds = a wound that takes longer to heal than basic HP damage. Characters suffering from a Lasting Wound have all base difficulties increased by one step (Average becomes Hard, or Hard becomes Challenging). If a TN is already specified, it is increased by 5. The healing times stated can be reduced by half (min one day) if the character rests and is attended by a skilled healer. If the character embarks on normal adventuring, the rest period doesn't take affect (you have to wait the full time listed to be healed).
1BP = Your attack inflicts a lasting wound that takes 3 days to heal.
2BP = Your attack inflicts a lasting wound that takes 1 week to heal.
3BP = Your attack inflicts a lasting wound that takes 2 weeks to heal.
4BP = Your attack inflicts a lasting wound that takes 1 month to heal.
5BP = Your attack inflicts a lasting wound that takes 3 months to heal.
Gritty but doesn't ruin the character.