Have you tried brining your breasts? That will add moisture (and flavor) to them and will guard against them drying out even if you over cook them. Just mix up some salt water (I don't measure, but it should taste like ocean water or maybe a little less salty) and soak then breasts in the fridge for 2-3 hours (but no more than that). Dry them off and cook however you want.
The other option is to get a probe thermometer. this will tell you exactly when the chicken is ready to come out of the oven.