Equipment is better for the back extensions and reverse hypers. Laying on the floor eliminates like 90% of the movement.
With good mornings, you should do them with proper form. I like to keep the reps higher and the weight a little lower. That's because my form goes to **** if the weight is higher than a 5 rep max. So I like to work with a challenging weight for 5-10 reps for several sets.
Try good mornings in all kinds of different ways. So long as you're working your spinal erectors and stuff you're fine. Try standing, straight legged, zercher, seated...whatever. They all have their benefits.