I have never made yogurt and don't know much about it. Regarding the boiling point of milk. I don't know off the top of my head, but would have to experiment with a thermometer. Below is a definition of boiling points:

Boiling points have been defined as the temperature at which something boils, but how does something boil? We can define boiling point in a better way. Boiling point can be defined as the temperature at which the vapor pressure of a substance is equal to the external pressure.

Altitude: Boiling points vary according to the barometric or atmospheric pressure. At higher altitudes where the mixture of gases we call our atmosphere is thinner, the boiling point will be lower since the external pressure is lower. At higher pressures the boiling point will be higher. At the boiling point the temperature remains constant until all of the liquid has been converted to the vapor state. All of the increased energy is used internally to convert liquid molecules to vapor molecules. For each thousand feet above sea level, the boiling point of liquids drops almost 2 degrees F.

Weather: The boiling point of is a degree or two lower on stormy, as opposed to fair, weather days. Consequently, boiled food will take longer to cook on a stormy day.

Different Size Pans: Will a given volume of liquid boil at a higher temperature in a tall, narrow pot than in a short, wide one? Yes. since the tall, narrow pot has a great depth, its bottom-lying liquid is under greater pressure from the liquid above it than is the liquid at the bottom of the short, wide pot. The greater the pressure, the high the boiling point. The difference is approximately 1 degree F.