Even if you're flat chested... if you go without a bra, we can still tell. What about a strapless bra? I mean... if you're considering going braless... its no different from switching from push ups to just plain bras that give you more flexibility in what to wear so that straps and such aren't showing.
You may as well go braless. Plus for fans of small boobs, there's nothing hotter. Don't worry about the push up bra, simply where something a little tighter than normal to show off your finest assets in ther small but perfect glory.