Just go with a Ruger LCP and whatever defensive ammo you can find with the Hornady XTP bullet. I am not a huge fan of .380, but ive never observed a round using an XTP bullet fail to feed or fire. The narrower profile and 90gr weight may have something to do with that.
If you wear long enough shirts, you can also pocket carry in your rear jeans pocket if you wanted. I am not sure if you are upright or bending over most of your time working?
I think using a Kydex pocket holster would be best for keeping dirt, sweat, etc away from your pistol. The nylon and leather ones would allow more dirt in I think and would retain sweat/water. Kydex snaps the pistol in place with a tight seal and you can quickly wipe plastic down each night.
I've had good success with this one when I needed a Kydex pocket holster:
http://www.vedderholsters.com/pocket-locker/
Good luck