We now have a Waitrose in Edinburgh - I discovered they sell lots of Duchy Original stuff, including:
Duchy Collection shampoo - (at least 2 "flavours"), sulphate free & all organic. Not cheap, but not extortionate - £4.95 for 200 ml.
I also like the following conditioner, very cheap indeed from Bodycare, smells wonderful:
Inecto Moisture Miracle Conditioner with coconut oil, 500ml bottle for around £2.
Body Shop Honey Moisturising Conditioner - more expensive, around £8 for 400ml. It does contain amodimethicone, but it's way down the ingredient list. Very thick and rich. There is a matching shampoo that is gentle.