Fage is better than the other brands of yoghurt and Able recommends it in his list of yoghurts. It has more probiotics than the other brands.
Dont buy commercial kefir. Buy your own grains to make up yourself from an individual who grows them and shares it out. I got mine from someone on ebay.
There are plenty of good UK online health food shops. I like Healthy Supplies and Luxe Beauty Company for when you cant get certain things in supermarkets. But there’s also iHerb who will ship to the UK.
I’ve been on this diet 5 months and there’s been nothing I havent been able to get hold of.