Oooh I used to say that. Then one morning the pain was TERRIBLE and I went to the emergency room, found kidney stones. They had, over months, blocked the urine flow so my right kidney was blown up like a nerf football (its called "hydronephrosis") and it gradually got better as I figured out how to prevent more stones (diet, water, lemonjuice).
SO I AM SO GLAD I HADNT SPENT THE THOUSAND DOLLARS ON A NEW MATTRESS YET, BECAUSE THE COST OF CLEARING MY STONES WAS $1900 PLUS WHATEVER MY INSURANCE PICKED UP. I don't think I could have afforded both at the same time.
I am 45 years old, some say with hormonal changes come kidney stones, and come to think of it, most of my kidney stone patients are around 40-60 years old (I'm a nurse).................
I hope your sore back is just a mattress problem. But it might be worth looking into if cost is a deciding factor. A cheap screen for kidney stones is a simple urinalysis, but a fun one is CT scan, because you can see and measure the size of the stones. ( That gives you bragging rights.)