Yeah, I think I know the reason for that. There should be a control script in CB which only allows certain Tits size on a selected race to appear. I might be able to increase that pool size to lower sizes, but not sure if it'll work for now.
If my solution will work somehow, I do plan to give starting races limited sizes starting with Flat. So on market you'll have:
Flat - Small - Average breast slaves. I'm not a fan of limiting stuff like this, but it will make user to actually breed for bigger sizes.
Since Cosmetic Potion will be unlocked on slaves - as soon as you open a brothel that won't be an issue anyway.
PootisPenser76
In the base game there's room upgrades from Barbara which can cure STDs when slave stays in a room for a set amount of time or you can buy potions which cures it at the end of the day (random drop). You can also create that potion with Niel, but you'll need to dismantle infected Slave/Monster for that first with Flora to get special infection DNA.