If you're using my 4-paragraph essay approach, your essays only need to contain two main ideas - one for each main body paragraph.
But there is a difference between the main idea and the supporting points. For example, the main idea could be "there are several advantages", and each advantage is a supporting point. Start a new paragraph for each main idea, but not for each supporting point.
Express your main idea for each paragraph in a 'topic sentence' at the beginning of the paragraph. Then explain that idea with either one, two or three supporting points.