If you want Michelins, I'd put two new Michelins on the rear and your 7mm Conti, along with a new one to match on the front. 7mm is as good as new, so there shouldn't be any imbalance at the front.
It is good practice to fit new tyres to the rear of a front wheel drive car, plus the Contis will wear faster on the front, meaning you'll be able to buy another pair of Michelins to match sooner, having got your moneys worth from the Contis.