You could try not using shampoo at all. I use bicarbonate of soda to clean and lemon juice to condition. Mix one tablespoon of bicarb in 300 ml of hot water Freshly boiled water works best). Rub into wet hair and then rinse. The lemon juice is two tablespoons in 300 ml hot water. Pour slowly over hair after bicarb wash, wait for a minute or two, then rinse off with cool water. It takes a bit of preparation and you need to let the mixtures cool before you use them. It's very effective and cheap, and you can be absolutely certain you know what's going onto your hair.