I would be careful in replacing springs as in that the 4 on your car will be "tuned" to your car, aftermarket springs may not be the same spring rate, etc,
VW probably list a multitude of different rear springs for a GTI alone taking into account if your cars 3dr, 5dr, non PP, PP, CS40, etc.
Yours will have splashes of paint on the coils to identify the spec of spring.
VW ones are about £90 each i think.