Seems your in a bit of a pickle then. If you refuse to lvl further and refuse to play other classes to unlock the cure spell, and earn other skills that raise your defenses like protect/shell/stoneskin, or even some DoTs like Bio/Poison. There are also skills from Marauder, Pugilist and Lancer that will return some HP to you as well. As it stands from what you've said though, you're SoL until you're willing to help yourself first and become properly prepared for that battle!