If the biggest bust is too small, then no, it doesnt look like theres anything that lets you become more voluptuous. I think this is largely due to the nature of the engine thats being used to make this and how the clothes are put together.
You can't change Sammy's thiccness unfortunately but you can change her Breast size at Dr. Nikolas lab but only after the first mission i think, and you have to pay, or you can just open the cheat menu at the top right of the screen and then just click customize and it opens the same menu.
