I've made my own yogurt plenty of times. I make a gallon or a half gallon at a time. What I do is bring the milk/cream mixture barely to a boil in a stainless steel pot, let it cool to about 45 C, then use a whisk to mix in 1 cup of room-temperature yogurt per half gallon of milk, wrap the pot thickly with insulating material (towels or whatever), then let it stand 6-8 hours, in a place free of any major vibration (on top of the fridge is too much vibration). I also use Bulgarian style yogurt because I like the flavor that its culture produces.
After 8 hours or whatever, the way you handle the yogurt is important. In India, where I grew up, a kind of clay wok-shaped pan is used for fermemtation. After fermentation, a few slices are made through the pan of yogurt, and some of the whey separates out into the crevices, making the resulting curds thicker. Here in the US, usually a thickening agent is added (pectin or powdered milk or something like that) and no whey is drained off. Easier for mass production, but I prefer letting some whey drain off.
In India, there is a drink, or kind of a milk shake, made with yogurt that hasn't had any whey drained off. They call it Lassi (rhymes with fussy). It's whisked or stirred, and salt and pepper added to it, or sugar and fruit or whatever. For thicker curds, you don't want to disturb it--handle gently.