Normally I would ask what the measurement from the top of your sternum to your belly-button would be, as when they have actual armor in them, the vest can jam up into your throat if the armor/vest is too long.
A "rule of thumb" is to buy the vest one size smaller than the t-shirt you wear. I have a 44-45" chest, and a Large CIRAS/LEO Carrier fits me great. I wear a medium, however, because a large is too long and when I sit, I get a chinful of armor/plates. I am 5'10, 225.
It also bangs into anything i am wearing on my trouser belt. A medium doesn't do this. That said, I did have to add longer paracord to the cummerbund adjustment of the LE Armor carrier in order to get the medium to fit more comfortably. I have a gap in coverage using a medium that I wouldn't have with a large.
All that said, based on your sizing, my guess is that a small would fit you better than a medium, partly because of the height issue. I have both a small and a medium in stock.
