You are wishing to conceal a service size handgun that must (absolutely must) never be seen by anyone around you while working. That will be virtually impossible to pull off.
I realize you wrote that it is the only firearm you can afford now, so this next bit of advice may be of limited utility. If you wish to carry a sidearm that will not be visible then the handgun will, by default, need to be of a much smaller size than your G23. I'd think something along the lines of a Ruger LCP or similar size handgun, carried in the strong side pocket in a good pocket holster.
Best of luck.