Thatbags I have bought any Easiyo yoghurt maker. They have Greek yoghurt culture/milk sachets which are excellent, prticularly with honey drizzled over. It makes a litre at a time - quite a lot but it lasts a week or so and if he likes it he will get through it. Sold by several people online, including Lakeland Plastics. Don't bother with the Starter Pack, which just has a using yoghurt recipe book and one sachet of culture, but costs almost twice what the older packaging of just the maker does.
Someone also buying sachets in Lakeland said that the Greek yog with coconut is even more delicious, but I have not tried that yet.
You just add cold water to the inner container, and boiling water to the outer, and leave it overnight.