If you have a Shimano RD, you can only use SRAM shifters that are 2:1 actuation ratio. Most SRAM shifters are 1:1 to work with SRAM RD's. Make sure you get 2:1. (The FD doesn't care which brand you use.)
Does your front fork and frame have disc brake tabs? Are your hubs disc hubs? You must answer yes to both questions for a straightforward change to disc brakes. Not usually cost-effective if the answers are no.