rear shocks

[oldgitofkent]

Hi hoping someone can help. I have a Decathlon rockrider which seems great for trail riding on a budget but being 15st i find the toughshock too soft with its 550lb spring but cant seem to find a comatible one with dim of 32ID/48OD/96L. Moving on the front seems very soft too These are SR Suntour CR forks. Can i get firmer springs
I am looking at a Rockshock RS bar2.1 at £106 if no joy with spring its the cheapest ok sounding i can find is air pretty low maintenance.
Any help or advice would greatly appreciated.
Cheers Shaun