The Blouse

I bought a new blouse that on someone else would show some cleavage. On me, there is no cleavage, so it just reveals an expanse of upper chest. The whole time I'm wearing it, I have to throw my shoulders way back and keep my chest inflated, or the top of it sags loose and you can see my bra. I like the color, and it looks good on me, but by the end of the day I'm just tired of having to stand up so straight. I can see the micro-flickers in people's eyes, too, flitting down from my face to my chest as they're talking to me to see if they can see anything. How do women who actually have cleavage deal with it?