Thanks Jill for response!! I checked out the websites you suggested unfortunately the NZ brands don't ship to Australia, seriously?!
and the Ethique: nourishedlife.com.au is quite expensive but we do have Etsy Aus, and even though I'm not familiar with the site I will have a look..what exactly determines I have the right product. Thanks for your help
Real soap, that is used for the body, no matter how gentle the ingredients, is far too alkaline for hair. Some people do a vinegar wash after shampooing with soap, to counter-act that, but - while on the Camino - that kind of negates the advantage of carrying just a hard bar for the hair. I've written a few long pieces here on the forum about soap vs shampoo, which you can find with a search.
What you want is called a syndet shampoo bar. I know that sounds artificial and chemically, but the ingredients are usually very gentle and are mostly plant-based. But it is a different process and does not use lye, which soap does (to be called "soap", it must involve saponifying fats with lye).
Yes, they often seem expensive, but the fact is that they will last far longer than bottled shampoo and are better for your hair. Lush is the most well-known commercial brand of bar shampoo, but their formulation includes some questionable ingredients and they tend to disintegrate faster than others (I've written about this elsewhere, too).
Especially if you have long hair that you want to preserve (and/or at least be able to get a comb through!), you should stay away from Dr. Bronners and other soaps or products that are made for use on the body.