Go with the Glock 27. It gives you the most compatibility: mags, parts, holsters, etc. The platform is exactly the same, thus the shooting characteristics will be as similar as possible given the size difference. If your coworkers also use the same sidearm, that gives you even more compatibility. I doubt things would ever get so bad that you needed your backup, but if you do the I'd say the Glock 27 would be your best option given that the 22 is your primary.