You could use warforged and warforged juggernaut (Eberron Campaign Setting) instead of human and bone knight. That gets immunity to nonlethal damage, critical hits, mind-affecting effects, death effects, necromancy effects, ability damage, and ability drain.
If your DM balks at a warforged having the troll-blooded feat, you can instead use renegade mastermaker (Races of Eberron) to qualify for warforged juggernaut.
If you go with warforged juggernaut, it'd be better to use half-dragon than void mind.
A troll-blooded half-dragon human that transforms himself into an unstoppable cyborg is kind of a cool idea.
