Immunity to damage is pretty nice. The only way I know is Trollblooded (feat from Dragon) which gets you Regeneration. Add Warforged Juggernaut 2, which gets you Immunity to Non-Lethal Damage. Now you just need Acid and Fire Immunity. It's nice to leave a loophole though, so I would just go Lawful Evil and Shape Soulmeld: Planar Chausuble for Resistance to Fire/Acid 10+5*essentia.

That last one is a little questionable... You may have to take two Soulmelds to get it to count. Don't take more than 2 levels of Juggernaut, it eventually removes your Con score which makes you ineligible for Trollblooded.

Paladin of Tyranny 2/Hexblade3/Warforged Juggernaut2/Binder1

is a nice start. Good saves, You may want to use Planar Touchstone: Catalogs of Enlightenment to grab that domain ability that allows rerolls of ones on saves. Immunity to most damage, Naeberius gives Ability Fast Healing, in case something tries to get you that way. Pretty much the only thing that can kill you is Falling Rocks.

If you can work in some Knight, you can make them swing ineffectually at you every turn.