Few of us in the real world have the bods for a bikini with a triangle top and a skimpy bottom, so just as with one-pieces, bikini makers have kept different bodies in mind. Bikinis often work better than a one-piece for women with a large bust and smaller hips, or vice versa, because you can buy different sizes in each. This is also a major plus for women with a long torso.
If you want to show some skin, but not all of it, look for bikinis that have good coverage and support on top. If you don't need that extra support, then an enhancer top might be for you. Even if your midriff isn't quite bikini ready, that doesn't mean you're destined for a one-piece; look for high-waist bottoms that come up over your stomach, preferably with some minimizer support.