Vrs Diesel hatchback rear shocks

Hi,

Has anyone just changed there rear shocks with after market ones and did it make any difference. My car VRS has covered 20,000 miles on a 15 plate. 

It seems to be getting harder on rear suspension when car has no weight in the boot. It feels like it pushes the car up with a jolt. Even the wife has commented on it. Makes it sound like the boot floor is loose, which is screwed down.

checked the usual things, leaks, transport blocks, bushes 

put 100 Kg in the boot and it's a different car. 

If you hit a bump at speed on a corner the back end wants to skip out. 

Feels like the shocks have lost something. I know they were not the best on these cars to start with. 

Any ideas.