I too have had the itchies and I have tried all the usual suspects to tame it and like you have resorted to poo. I bought a low poo on line and am using that at the moment and so far it seems to be working. I have included a link to their site it advertises as using no sodium laurel sulphate www.skinshop.co.uk
The shampoo and conditioner I use are from their Dry Scalp Range. My scalp gets little build ups of skin that then itch and if it gets bad they fall off and bleed and it drives me insane. I used the Giovanni Tea Tree and it did nothing it might work for you. They sell trial sizes on E bay. At the moment I had decided it is more important to get my scalp right. I might try co washing again if it clears up. Sometimes you just have to do what is right for yourself and no matter how good it sounds going CG for some of us the scalp issues are just too severe. Let me know how you get on and remember if you use a low poo its not the end of the world just use a DT once a week.