Just started to make my own yogurt, always been put off by all the expensive looking stuff you need (double lined boilers, starters, powdered milk, cooking thermometers ect) it never rang true, on the streets of India they make them fresh each day with no more technology than a large frying pan and open fire. Then I read you could make yogurt in a thermos, so with a little variation I had a pop.
Thermos are pretty small so I bought a cheap plastic 1.5 litre Ice Bucket at a pound shop, you also need a pot and a spoon.
Here's the method I use.
Boil water in the pot, pour it into the thermos and dip the spoon in to sterilise everything.
Next put a litre of milk in the pot and heat up until the first sign of boiling to kill any bacteria in it. Stir continually to stop the milk at the bottom burning.
Let it cool stirring regularly. After after a while stick your finger in it, if it burns immediately its to too, if it burns after a second of so it's ok, if it doesn't burn it's too cool. The cooling is around 10-15 minutes.
Put a small pot of plain yogurt in the ice bucket as a starter culture (first time you do this) Next time don't eat all the yogurt you make, leave 2 tablespoonfuls as starter for the next yogurt (it called a rolling culture).
Mix a few tablespoons of the milk with the yogurt in the ice bucket so its liquid. Pour the rest of the milk in and stir well.
Wrap the ice bucket up in a towel and a plastic bag. Put it in the warmest place in the house and leave it a minimum of six hours but preferably longer.
It's much fresher than supermarket yogurt so will keep for ages in the fridge, but after a week will start to decline in quality as a starter.
Yogurt you make yourself tastes much better. Also you can experiment with milk types. and it's so easy you could make it on a camp fire in the evening and have it for breakfast in the morning.
If you want thick yogurt strain it in a cloth so the whey drains from the curds.