This PJ set is cute and fun to lounge around in. I most definitely would size up- mostly because of the bottoms. The reason being is that the fabric on these does not stretch. There is no give in the fabric, which makes sleeping in them sometimes uncomfortable. Maybe I'm a wild sleeper, but if the top gets twisted some from rolling over, for example, I wake up to trying to straighten the shirt back as the fabric just doesn't move with you- like a soft cotton knit would do. This fabric is truly like a button up dress shirt.