In Stable Diffusion, use “curvy, busty, perky”, and in negative prompts use “fat, overweight, saggy” to get the largest, perkiest breasts possible.
But huge fake boobs require its own training set. There are some in the wild that are trained on bimbo 3D artists that are then re-mixed with photorealistic images to turn them into reality.
But there is no online service that offers that
