I'm a guy that's tall and thin. I got tired of the trash bag look. I get custom fitted shirts made to my size. There are many online tailors in China that will make a duplicate of a good fitting shirt, or one to your size preferences.

There are many aspects to a properly fitted shirt. If the shirt comes untucked when you raise your arms, it's probably because the arm hole (where the sleeve attaches to the torso part) is too big.

Costs more, but worth it if you're having trouble getting a good fit.