I'm 5'6" 170. Most of its around my belly. I wear a suit at work and would get fired for bring a gun into the building any way. IWB doesn't appeal to me.  What some options for part-time carry including some sort of in-car mount. I'm looking mainly at single stack 9mm's e.g. M&P Shield, Sig P225 or Walther CCP. I'm also looking at a SIg P320 either compact or carry.

Confidant Shirt

If you have your job on the line and simply cannot do without a firearm on your person while at work (not condemning you in any way) then the smartest solution would be to invest in a very small pocket auto such as a LCP and carry it on your person with ease... In the pocket, ankle, belly band, wallet holster, ect... This would be a very incognito option

I understand people want to carry a 9mm at the minimum, but how high of a threat area is your place of employment?

Just a side note, in NC if you are found out you could permanently lose your carry permit and the ability to purchase handguns.

Losing a job is bad enough but that's just the tip of the iceberg. Don't forget work history checks by future employers.

It's far more likely that an "oops" at work will out you as a concealed carrier than the actual need for a self defense use.

^this^
I carry a Ruger LCP during summer months when its more difficult to conceal wearing less clothing. I am built similar to OP and am in a similar work environment. I carry that pocket pistol with nearly as much confidence as my winter EDC .40cal I know how to shoot it and shoot it well. Lets face it 7 well placed "defense" rounds from a .380 or hell even a 22 will effectively remove the threat. Of course a larger caliber is advisable but if the environment doesn't allow for it .380 is better than hiding under a desk.

If your workplace doesn't allow firearms, you should consider some less-lethal but less regulated options.  

If you do decide to carry a pistol, a J-frame in a pocket holster is the best combination of concealed, convenient, and capable that I have found in 15 years of looking for the next best thing. A pocket holster will be less awkward than some OWB/IWB options if you decide to leave it in the car while at work.  I bought a pre-owned 642 for $300 and it has become my grab & go weapon despite a safe full of Glocks, M&Ps, and 1911s. It's not sexy or tacti-cool, but it's simple, reliable, and comfortable.

As has already been mentioned the smaller the better in your circumstance. The LCP is a fine choice or something of similar size and weight. Also while suit jackets give nice coverage, suit materials don't obscure as well as something like denim. You might want to look into something link a belly band or thunderwear or something like that. While those may not be as easily accessible it may lessen the chances that you'll be made.

I'm actually looking for a carry option when not at work. I wouldn't dare walk into my office with a gun. I anticipate that much of my "carry" would involving accessibility while in the car. Carry on my person would be strictly limited to off-work hours.

Went through a rough period at work with layoffs etc. Since I worked within 10 feet of the front door, I got 2 different guns for deep concielment.

First was an NAA .22 LR and later their .32 ACP (more firepower ).

Both were pocket carry and since I only had a 10 feet buffer with my back to the door, either would take care of things!

I was pretty well liked and hourly, so it was more likely I would not be a target...

Nothing ever happened but those little guys sure made me feel better.

Ive been fired for carrying a gun at work..not fun. I make do with a CRKT pocketknife and an Olight 300 lumen clipped to my weak side pocket now and a blow out kit in my backpack.

A belly band and LCP would be the way to go IMO.

Take a look at some of the single clip kydex holsters. Being in IL I have to deal with disarming to go in some places. Easy to take the entire holster off and put it somewhere in the car.

Have a bunch of the Vedder lighttucks that work well for this. PJ is good too, but their standard ride height is a bit low (need to ask for a bit higher on my next one).