Help with buttons on a sweater

Hi.
While you can create texture-based buttons of appropriate size by painting them over in Blender, the one in the chest area will still stretch when the breast are made bigger. You could try painting the breasts with 3fff00 (read only the quoted area) but it will still happen to an extent.
Here is an example of how to paint on the mesh (you just need to export your top and paint on it instead of the head)


If you were to make sculpted buttons, the one in the chest area will still stretch with the breasts morphs.

For the newly created geometry to conform to the rest of the outfit, it must be rigged, vertex painted, have uv_1.
To avoid doing this, you could projects a circle on the surface of the top, then use Weld edges into shape to carve it into the surface. Then you could extrude and unwrap it.
Both of these options require basic understanding of mesh editing and blender interface, so you would need to watch a tutorial on mesh editing first.