There is also this amazing product called Fit Control for Genesis 8 Female (there is a version for male as well, and a bundle with both):
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You must be registered to see the links
And even an add-on:
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It's available on the forums last I checked.
I use it almost everytime I have such problems as you posted, in particular around the chest area and under it. It is very powerfull.
What this product does is it adds a bunch of morphs to any clothing piece of your choice (you get a window where you can pick the pieces to add morphs to).
It does have a few problems thou.
If you character has hair loaded on it, using this product's script may result in daz appearing as if it locked up (it didn't, it's just a problem with the script). To avoid that problem, make sure you have no hair loaded before using the script.
So I recommend you use it before you load the hair. Or, if you have a saved character, make sure you save the hair as a wearable preset, delete it, use the script, then load the hair, it will save you many Many minutes.
Second, using this product will make your save file get bigger, because the new morphs are saved in it. So if you have enought free space, it's all good, but if not then make sure you do. Another solution to this is tosave all the new morphs, and in doing so, they will become "attached" to the clothing item, and not to the save file.
In anycase, I personally use this alot, even have it as custom action, so I recommend it, just keep in mind the things I said, no hair to save time, and keep an eye on your free space. Otherwise, between the basic product, and the add-on, there are tons of morphs to fix any fitting problem.