We are going to write a whole article about the topic on our blog soon because it's been quite the little journey for us. As performance artists, we have to do stage make-up and hair for shows but still want to be more eco-friendly and practical for moving into a cargo trailer soon.
To sum up our experience so far: I have very fine, long, straight hair and can wash it with Dr. Bronner's liquid Castile soap and condition with apple cider vinegar with no issues. It looks just as good as with shampoo and conditioner, even with a bleached stripe that I color bright red or purple (soap isn't kind to color, however).
My partner in all things and fiancee on the other hand has thick hair that is a bit wavier. She cannot use soap without coming out too oily after several months of trying (as well as trying the rye flour option). We found her a shampoo based on cocamidopropyl betaine, which seems to be a gentle, less-toxic and biodegradable option in the same family of chemicals as most surfactants. I'm pretty comfortable with chemicals (having done organic chem in college) and can't really say much about toxic substances in my body because I eat fire on a regular basis for shows (fuel isn't good for you). However, it seems to have a good eco-toxicity profile so far. The one she is using for now is Kiss My Face Whenever. We'll know more after some time passes, and that will be in our article. Overall, different people seem to have different results.
-Brooke