Concealing a 1911 in a T shirt.
It can be done, I've done it. Get a good IWB holster. Several makers have good options. Carry the gun behind the point of your hip, the grip fits near the small of your back, aiding concealment.
Get your T shirts one size bigger, unless you're already wearing them loose. Get relatively stiff material, no cheap two dollar shirts, the thin cotton prints badly. Dark colors help, also. Prints or designs, even just logos on the front/back help, it draws peoples eyes away from your waistline.
Don't bother with a "tuckable" for a 1911. Your shirt will have to be bloused out so much you'll look like a Cossack dancer. Get a holster with a foreward cant, it lessens the length of the grip along your waist.