If you make it so concealable that its impractical to get to if you needed it quick you might as well leave it in the car. I only say that because some of the options mentioned by other members are quite ridiculous.
The only way to find out what works best for you, in your own situation, is to try as many different things as you possibly can, and pick what works best for you. There is really no other way. If you want to carry a gun, without fail, you need to figure out how to do it. Its really not hard, IF you want to do it, but you do have to put in the time and effort to figure it out. And its not likely going to be cheap in the long run either.
Ive carried pretty much every possible way you can think up, at some point over the years, and found some things work great, and some dont. Some are limited to just one type of carry for specific situations, others work well in many different situations.
The one thing that is a constant across all of them is, you have to actually try (and give it a good try) whatever it is you think might work, and prove it wrong or right, "for you". It doesnt mean crap if it does or doesnt work for someone else. It has to work for you.
Ive carried a full-size handgun daily, and on many, if not most occasions, a back up as well, and with reloads for both. Im constantly told I couldnt possibly carry a full sized gun, by people who only carry a little, third line back up as a primary. I have never had any troubles doing so, they obviously have a different experience. But due to my experiences, I have to question if they really ever tried. But thats besides the point, its what works for them, and it works for me. Or, at least it has for the past 45 years or so.
Holster types I have used in the OP 's "office"/NPE type environments have been the undershirt type holsters, ankle holsters, and the Smart Carry holsters. All worked fine too. And with practice and some understanding, the gun can be easily accessed and deployed.
Of those three types, I find the Smart Carry's to be the best choice for me. Very comfortable for 12-18 hour use, in pretty much all environments. Allows for a realistic gun to be carried in deep concealment. Quick, easy access from pretty much any position. And easily removed or put on, if that should need to happen. And the least likely to be noticed or discovered across most circumstances.
To give you an example here as to how well they work, I got bushwhacked into a drug test with no chance of ditching my BUG (left my primary in the truck when I went in), and had to empty all my pockets, take off my shirt (still had a tee on), unbutton my pants, etc, all in the presence and watchful eye of the nurse, for the test. She never noticed my 26 and its reload or the holster.
Some things may seem silly or undoable at first glance, but youll never know until you actually try them out and can prove them one way or the other.
Sorry to say that I have not even been carrying for the past 27 days. Something I have done for the past 10 years. 27 days ago I missed renewing my CCW permit by two days. Now have to go through a 45 day wait process. I have always concealed and wear all my shirts etc. like the one's mentioned above. I am of medium Height, medium build, no paunch etc. Just hate to tuck in a shirt and just cannot find a solution for outside carry. It is amazing how the feeling of a certain right is taken away due to Bureaucracy. The thing is, I have not even had so much as a parking ticket in decades. Why can't someone get a drivers license renewed so quickly yet a responsible gun owner would take this long? It is what it is, so I am just sucking it up.
If I do get killed by a bad guy while not being able to defend myself, I will be even more upset. If I do have to go down that way, I would much prefer to go down fighting. Never thought that open carry would suck so much. I do carry mace now and a Knife for quick use.
And what is interesting is the fact that I have purchased two firearms in the 27 days with no problem and fast service.
The way Ive always looked at carry permits is, they are a "learning permit" that allows you to learn to carry the gun and its accessories properly, in relative safety from reprisals, until you are comfortable enough that even without a permit, or should you end up someplace you shouldnt have the gun along, you wont give it a second thought and wont get caught.
That way when if and when they should decide to take back the "permission" they gave you to exercise your right, youre already well trained and good to go.