You really need to move to appendix IWB carry (AWIB)..............& with a loose fitting T-shirt it will conceal with a decent sized gun better than anything else.

And get yourself a S&W M&P 2.0 Compact with a 3.6" barrel & forget about the Glocks as the footprint of the M&P is much easier to conceal & it's a full size grip, 15 round gun.

This is the holster, below, that you need & pics of the M&P 2.0 Compact in it. (It comes standard with a "wing" which pushes the gun butt in tighter to your body)

Appendix carry for some takes a little getting used to & you may have to make yourself work at it in the beginning....................after a few days, you'll likely never want anything else.

It conceals better, has faster access standing or sitting & is easy to sit with for vehicle use.

But correct fit clothing is important............loose fit doesn't need to be 2 sizes too big, just a matter of how it's cut. Not all shirts are cut the same.

MM

TXC Holster

Model X1 TXC holster with 3.6" barrel M& P Compact 2.0

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]