This is really easy and a great way to make yoghurt in bulk. If your family is anything like mine, you go through yoghurt at the rate of knots and it gets expensive! This yoghurt basically costs the price of the milk you use, especially if you keep a small little bit back to start your next batch. You will need a food thermometer to test the temperature of the milk. These are easily available in kitchen shops.
I use whole milk because I’m a full fat kind of girl. I haven’t tried it with skim milk but I reckon it would work just fine.