This can be done on any difficulty. It's much easier on normal as your health regenerates after each combat encounter. But on the harder difficulties try using Bormins and Farrows corpse eater if they take damage. You can also skip as much of the combat as you need by sneaking by enemies in the DLC. The achievement should unlock right after you defeat Jyko so you can always back track to get the collectables, side-missions etc. afterwards to not have to worry about not healing.