/3/ - 3DCG

>>553927
that's one way you could do it. I kinda struggle with creases as well, so I'm probably not the best person to answer this but what I do is sculpt (the breast in this case) as a separate object, then merge it onto the ribcage. The problem is that when remeshing they might weld together and you will need to redefine the crease with a thin brush.

I suggest you look for sculpting videos on youtube and pay attention to how artists sculpt the nose, the space between the nostril and the cheek in particular, which also creases. You might be able to adapt the same techniques.