Defense shifters are good for solo exploration. If you have regen form (major komodo/rattlesnake or lizards/copperhead), you can do a lot with retreat -> heal fast -> reengage. Maybe you can switch major/minor to make it faster. I don't know about OG though, maybe they are better.

Wights don't need an item quest and they have tons of different immunities. They are good for exploring almost everything (well, mummies are good at that, and I suppose wights aren't worse). It's difficult for necros to take down supertough mobs that hits everyone fighting them. Or do area spells often. But in 99% you'll be okay.