While I haven't been in your situation, I have given a lot of thought to what I would do if I needed to carry for maximum concealment.
I normally carry my 642 IWB at around 3:30-4:00. Under my typical clothing it is practically invisible, even if I have to bend over to pick something up. However, there is the possibility that I might not be able to wear an untucked shirt. Then again, if I can't wear an untucked shirt, chances are I'm someplace that prohibits carrying a gun.
I haven't tried Smart Carry, but I'm not comfortable with its accessibility (or lack thereof).
I have similar concerns with ankle carry, although it does offer some advantages if you spend much of your time sitting. I carry a small trauma kit in an ankle holster, and with my usual jeans it disappears. I never cross that leg. But accessing a gun quickly can be a problem in any non-sitting position.
I've never tried a holster shirt, so I can't comment on that, except to say that unless you have a lightweight gun and wear the shirt very tight you may have to deal with the gun bouncing against you as you move. I would have similar concerns with something like an upside-down shoulder holster worn under a shirt (something I have considered). Something like a belly band or Kangaroo holster may be an acceptable alternative.
For me, at least, if I couldn't get away with carrying my 642 IWB under an untucked shirt, my first choice would be something like a LCP in a pocket holster. I think that combination would give me the best balance between concealability and accessibility, while acknowledging it has its weaknesses, most noticeably drawing while seated. YMMV.
As has been said, whatever carry method you use will involve compromises in one way or another. You may just have to experiment to find the compromise that works best for you.
Just my opinion.
. Good luck in your decision.
