I'm curious to see what you find, but I suspect Energy resistance is really going to turn out to be the only path. Fortunately, with the new enhancement sets on Rebirth, even starting from 0, you can get pretty decent resistance on almost any build.
Gauntleted Fist will give you your first 6% energy rez bonus, so you likely only need four more. I like splitting up Vampire's Bite into 3 sets of 2 pieces to snatch another 3, 6% bonuses. If you have anything that can slot witchraft you can get another 6% bonuses. If you have over 5, you can always leave the Halloween enhancements unenhanced for the 4.5% bonus. (Fear and Resurrect can get the bonus with fewer slots, but those a bit more niche).
Then for the rest of the 4.5% bonuses, I like slotting shield walls in powers that can be slotted for defense since you only need four of them:
https://wiki.cityofheroesrebirth.com/wiki/Category:Sets_that_improve_Energy_ResistanceIf you can do the 5, 6% bonuses and 5, 4.5% bonuses, you can hit 52.5 energy resistance and then add in Shield Wall and Reactive Defenses Globals and you're at 60%. So even if you can't hit the full 5 bonuses, you can stack substantial energy resistance.