I make yoghurt without any commercial yoghurt makers. You will need a small pot of plain yog to start with.
Use a 2 litre plastic jug with a lid. Put 1 litre of semi-skimmed milk into jug; place jug in micro-wave for 3-4 minutes; leave to stand for an hour, Stir in two tablespoons of dried milk powder and a generous tablespoon of plain (bought) yoghurt. Put lid on jug and put into the airing cupboard until the morning. That's it. Done. Delicious.