What will help my lower back while standing at work for 8 hours?

I just started working, and I'm cashiering. We stand around a lot. I normally work 9 hours on the weekends and my lower back is in pain after 6 hours. I'm like 5'8'' so I do hutch over a lot especially when I'm working at the cashier. I don't want to use anything that has heat because its too hot in the store and outside. I've never had anything like this happen probably since I've never worked. What could I use?