I know you said that you're protein sensitive, but honestly, protein is the only thing that might be able to help your highlighted hair regain its curl. As someone who is familiar with color and bleach, I learned quickly that if I wanted to keep my hair on my head, I had to step up the amount of protein I used. My go to product is ApHogee's two step treatment. It's not meant to be used on a regular basis, just every 6-8 weeks at the earliest. In between treatments, find yourself a good moisturizing deep conditioner for weekly use, and a lighter protein based one that you can rotate in as needed.
If your damage isn't that bad, you might be able to get away with something a bit milder. It just depends on what you think is best.