Seated good mornings are an excellent lower back exercise. It will also hit your erectors and traps very hard. Seated good mornings effectively remove most glute and hamstring activation that are prevalent in the standard good morning. To perform this movement, sit down on something, be it a squat box, a bench, whatever, as long as it's not a bosu ball. Make sure your thighs are parallel to the ground, like you would be at the bottom of a squat. Now do a good morning as usual. Don't go so deep that the barbell rolls over your head and onto the floor.