Pi do a good range of springs, pretty sure they will have some for a bardge of a 7 series
Springs will stiffen the car, but at the same time lower it. Get airborn again and chances are the same is going to happen due to the cars weight. To stop it bottoming out, you will need uprated shocks - good quality bump stops may also do the job, but that is a pretty big mass of metal...
Pi are the not the hardest springs in the world and will(as Stuy said) not stop it bottoming out over jumps.You could also try Eibach or H&R springs but you will need uprated springs or it will overbounce all over the place