So I've got like a D small DD Cheatse's but yeah.
Okay here goes.. & I'm gettin' yelled at by my other T guy friends as I write this...
If you've already got a binder but it's not tight enough; Wide ace Bandage or tight sports bra. Make sure you pull the bra all the way down to flatten not hold up your cheaste's. If using a bandage make sure to wrap the top then pull your binder over. Sports Bra usually works way better, it gives you a peck look. from here you can either layer or just a shirt no larger them a SINGLE size bigger then what is form fitting. Remember too large, or too small SHOWS CURVES, you don't want that.
If you don't have a binder; Sports bra, pulled down like before, then a cheap neoprene back "support" really cheap like two bucks cheap, then a tight under armour shirt, dugee or tank top.
Another option, the best in my opinion for a flat chest is a medical supply surgical abdominal binder. It's velcro and creates an extremely flat chest. it isn't completely realistic but it's flat.
My favorite realistic looking chest is get an underworks 997 a size smaller then your measurements works well, and as always PULL DOWN AND TO THE SIDES, looks like pecks, if you've got a stout active looking male body.
But seriously, take this into effect... PLEASE DON'T BIND INTENSELY FOR MORE THEN SIX HOURS! seriously even that long is pushing it. Simple binding for small chests for eight hours is NO BUENO. So at the six hour mark peel that sucker off cough a couple times and leave it off for at least thirty minutes.