It doesn't need to be very warm. A little warmer than body temp is about right. You can warm the oven to 250, then put your jars in and turn the heat off. Leave the door shut overnight (no peeking, it lowers the temp). Or you could find some counter space and set your jars on top of a heating pad.
Homemade yogurt made with whole milk is a wonderful treat, especially with a little vanilla, sugar and fresh strawberries.
Remember to save out a half cup of each batch to use as starter for the next.
Be very clean when you're making yogurt. Basically you're culturing bacteria and where the good ones can grow so can the bad. That's why you scald the milk and sterilize the jars. After you pour the water off homemade yogurt should look and smell like yogurt (maybe a little stronger because you're smelling it warm when store bought yogurt is always cold). If you have any doubts, dump it. I've only had one batch go bad over many years of making yogurt and when I smelled it there was no doubt that something had gone very wrong.
Kathleen