I highly recommend that you consider the pie crust recipe developed by food scientist J. Kenji Lopez-Alt when he was working for America's Test Kitchen. It uses a combination of butter and vegetable shortening:
But the really important ingredient is vodka, which adds moisture without triggering the development of too much gluten in the crust. Here's a detailed explanation of why he chose a combination of fats, and why he used vodka in place of some of the water: