... I'm trying to play dead is dead with this character ...
My first thought is to abandon the one-hit spell, as gpstr suggested, in favor of a milder, two- or three-hit spell.
My second is ... hmmm ... it might be time to rethink the dead is dead strategy.
IME, dead is dead is an interesting but extremely difficult roleplay. Last year I tried this several times, after hearing others describe how much fun it was right on this forum

, but I never got beyond level 12 to 15 (IIR) (see my sig for the mods I play). It does force the player take full advantage of every single resource. It's a challenge, but often to the point of being aggravating. Anytime a roleplay becomes aggravating, it's time to rethink the roleplay.
Without some limitation, I, too, find the game a bit boring. When dead is dead didn't work out, I came up with my own solution: 9 Lives. (You can use any number other than 9, of course; I now use a random number generator and pick a number between 1 and 20, and that's the number of lives I get). I keep track of them meticulously, with a .txt file on my desktop, and when I die, I raise the number (0/12 becomes 1/12 and so on). Basically, it allows me the flexibility not to have to abandon a character just because I didn't see that gargoyle in the corner.
But if you really want to do this and use that spell, you'll need to find/enchant reflect/absorb spells/armor/clothing. Resist magic and dispel on self are your friends. Also, you might want to keep a few fortify health spells around just in case you're not to sure ....
Good luck.
~ Dani ~