I work with a lot of Indians (dot, not feather) and I asked a coworker how he makes yogurt.
Very simple stuff.
1. Full fat Vit D milk. Heat a gallon to almost, but not quite, boiling on your stove very slowly, while stirring to prevent any burning.
You can add some powdered milk at this point, if you want it thicker. You don't have to, and frankly I didn't feel like it did much for it.
2. Let it cool to room temp.
3. Add a spoon full of your last batch of yogurt OR some store bought active culture yogurt. Very very important its active culture, you need those cultures. You can also buy just the cultures online, if you really want, but its way cheaper to just get a pint of active culture yogurt at the grocery.
Stir in that culture.
4. Put on a lid.
5. Put it in your oven, with the oven off but the oven light on. You have to use a normal oven with a normal 40 watt incandescent oven light, none of this fancy pants new fangled stuff with LED lights. You need the warmth from the light. Make sure the door is shut.
6. Let it sit 18-24 hours.
Congrats, you have yogurt!
If you want it thicker, strain it in a flour sack or cheese cloth.