soft suspension - springs or shocks ?

hi

I have noticed lately that my 1999 E240 (w210) elegance suspension seems to be rather soft and the car wanders on the road all .

The suspension is very easily pressed down on all 4 corners and bounds back to level after about 2 bounces

Early last year i got all 4 shocks replaced ( bought from GSF ) and there was an improvement so I'am just wondering

1. is there a definitive test to determine if its the shock or spring that require replacement.

2 looking at maybe firming up the ride a little ( not to avantgarde level) what combination of shocks/springs would be recommended ?

thanks in advance

brendan