Here's an easy recipe for making your own yoghurt.
Boil 1 1/2 litres of whole milk.
Cool the milk to 45 C
Add 250 ml plain yoghurt.
Add 1 teaspoon vanilla essence.
Mix, pour into a container and keep warm for 10 - 12 hours.
I place my container on top of a radiator and drape a towel over it to keep the heat in.
If you save the last 250 ml of your home made yoghurt each time to make your next batch you will never have to buy yoghurt again.