Simplest way to make your own yogurt

I like to eat plain whole milk yogurt. There aren't many options. In most of the grocery stores, the plain Greek yogurt is the only choice. It has too much fat. I’ve started trying to make my own yogurt a few years ago. I've tried many methods. Now, I've found the simplest way to make my own yogurt. Pour whole milk into a cup, microwave it for a minute. After taking it out, add a small spoonful of Greek yogurt, stir it. Cover the cup with a paper napkin. I use a rubber band to secure the napkin. Leave it at room temperature for three to four days, and the yogurt is ready to eat! It will be a bit thinner after three days; much thicker after four days. The microwave time can be adjusted slightly depending on the cup's size and the microwave model.