Actually, the chainmail T-shirt is quick and easy to put on: accordion-fold it, raise it over your head with hands in the armholes, and let it drop. The quick way to take it off is to bend over as if you were going to touch your toes, and let it slide off down your arms. It will naturally accordion-fold into the configuration for putting it on.
By the way, in Marvel Comics you often see Conan wearing a mail-vest type of armour. I havent been able to find a pic yet. But it is open in the middle and with shoulders unarmored, length to the waist so the end is hidden by the belt.
This vest perhaps you can put on fast and unassisted, like you would a jacket. But would it be practical to wear?
But of course, it doesn't show off your "cleavage" and "guns" as does the vest you describe.
Sounds like a nice thing to wear in the summer.