What are some comfortable shoes for working retail?

I am working currently at Bed Bath and Beyond, and we are only allowed to wear flat soled, closed toed shoes. I am constantly up and down a ladder, so its pretty much mandatory that i wear sneakers, or some girls even wear things like uggs, especially since its getting cold out. I've tried many different sneakers, from Pumas, to nikes, adidas, asic, and danskin, ive tried putting insoles in them, and still after a 9 hour shift, i can barely walk because my feet and back hurt so badly. I'm truely miserable. What are some really comfortable shoes that won't hurt my feet, or back after a 9 hour shift that i can still go up and down a ladder with?