Softer rear spring rate for light weight?

Hey all. I am looking to soften up the ride on my 03. I am a tall skinny guy weighing in at 165lbs and 6ft. The fork seems to do a great job, but I get beat up from the back. The stock rear springs are already at their lowest setting. Any advice? I'm looking to stay stock with very limited 2-up riding. My wife is tiny so softer springs won't be a bid deal.

Thanks