Each generation has its own strengths and weaknesses.

One of the reasons for the changes between Genesis 1 (Victoria 5) and its single figure and Genesis 2 (Victoria 6) split gender figures is so clothing could be better made to fit the adult female form.

In the real world if you put a shirt that was tailored for a woman with a large chest onto a woman with a flat chest, it isn't going to fit right. Depending on how the clothing is modeled you will run into the same thing in the 3D world.

Like the real world (where you can hire a good tailor) there are solutions in the 3D world. The first thing to try is Collision and Smoothing. (Though if you have to turn smoothing up beyond 4, that is unlikely to be a good alternative.) Select the clothing, go to edit-> geometry->.apply smoothing modifier. You can then make adjustments in the parameters pane. Instead of, or in addition to that, Zev0 has a product for called Fit Control for Genesis and Genesis 2 Female(s) which adds morphs to the clothing, 3 of them are specifically to help smooth out the chest area for a flat chest. You can use a modeler (like Hexagon) to add a morph to clothing to give you the exact look you want.

The one that requires the least work, on your part, though is to use a figure and supporting clothing that is closer to what you are looking for. For example virtually all the clothing made for Genesis 1 was modeled on a figure with a flat chest. Which would mean that the clothing would not have to be adjusted to fit a shape it wasn't designed for, in your case. Genesis 1 base has a Basic Child Morph which is very similar to the Genesis 2 Female Youth Morph that comes with it. Combine that with other morphs and you have close to what you are describing without the clothing issue.