Upvote:4
As already suggested in the previous comments, SAVDA provides a one-change connection from Courmayeur to Milan.
You can find the schedule and other info here.
Since you are not familiar with the Italian language, I will report some significant information below:
It should be not a problem to find three seats. I would suggest being at the bus station in advance, just to be sure and be able to choose the seats (I believe half an hour is more than enough, but ask the travel agency).