I heat whole milk to 180 F, let it cool, then let it cool to 110 F and put it in a sterilized jar with a bit of Noosa (Australian) yogurt when I need a new starter. I then put the jar(s) in a water bath in my slow cooker, with the slow cooker hooked up to a Dork Sous Vide temperature control, which keeps the water bath exactly 110 F, and after about 12 hours the yogurt is insanely thick.
Sometimes the yogurt just tastes like cooked milk, so I don't know if I'm overheating the milk or what I'm doing wrong. Sometimes it tastes perfect, like a half gallon of Noosa for $5 instead of ~$24. I've heard you can use shelf-stable milk like Parmalat and skip the heating phase, so maybe I'll try that.
But I've definitely found that measuring and controlling the culturing temperature, and sterilizing the jars, to consistently product super-thick yogurt without the need to strain it.