It might just be me, but I haven't found a way to boost Sara to her absolute maximum size and still get the best ending.
Here's the things I do know on how to increase her breast size:
- Use the Raygun on her (or entice her to using it on herself)
- Read the delivered book in the lounge
- Read the idol incantation
- Give Meloni all of the fertilizer and the bottles from the sitting room (+3 sizes)
- Wish for bigger breasts with Lustra (locks you out rescuing Lilith for best ending)
So I'm wondering if there's something I'm missing. Especially since it feels a little disappointing that you can't get both maximum size and best ending.
Unless giving Meloni breast milk (before fertilizer) is supposed to make it +4 sizes and it's just not working.