Which Shampoo and Conditioner, UK?

Ok, I don't doubt this question has been asked a thousand times on here and I HAVE searched through previous posts but I'm not finding the answer I'm after.

I'm hearing so many contrasting things regarding shampoo's and conditioners for extensions. I've heard that you should use PH Balanced and they'll be fine, Soya Shampoo keeps them wonderfully soft, any shampoo apart from strong and harsh ones (!) and 'only use VERY specific ones' (not buying the latter). Also, diluting in a cup for a week with a sample of your hair to see how it takes!

So, what do you recommend? My clients all use gentle shampoos as advised. However, I'm just determined to get to the bottom of this to see if I'm missing out on anything fabulous. Especially after hearing that some products can enhance a blonde! And is there a no-go?

Many thanks