Small of Back carry presents a few problems. They are comfortable, and conceal very well when you are standing.
However, when you sit, stoop, or otherwise bend, they tend to stick out like a massive tumor on your back. Also, the cover garment is likely to ride over the grip and get caught, leaving your gun exposed for all to see. Lastly, the can be very uncomfortable to sit with one one, since you will be resting your weight against it, pressing the gun into your back.
Please consider all this before you buy SoB. They are nice in theory, but I find it very uncomfortable, as do many others. I'm not saying you can't do it, but think about how you spend much of your time, and what problems that might present themselves to you in your day.