I'm not really sure what the Sissy culture is all about but I think I understand what you are asking for.
I found that PM serum will swell the breast a little, temporarily, like for a couple of hours or so. I never really timed it.
So, if I were going to go out or just taking some pictures, this would be helpful. I think. Never know how it works for someone else.
Then it will go back to its previous state. However, if you do this every day, it will gradually build up and remain permanent.
If you do not have any boobs or moobs, this may have very little effect for you. The smaller your boobs, the smaller the effect.
I used the Swiss Botany brand PM serum in the pump bottle. Massage one pump into your breasts.
Use rubber gloves so that all of the serum is absorbed by your breasts, not your hands because you want the localized effect.
https://www.swissbotany.com/products/pueraria-mirifica-serum
Then you can use a Noogleberry type pump to increase the effect, though I am not a fan of this technique.
I feel that this can cause undesirable, permanent tissue stretching that will later lead to unattractive sagging or mis-shapen breasts.
My caution would be to use only enough vacuum to keep cups on firmly and not to the point of your boobs turning purple.
If it hurts, it's too much vacuum. Only leave them on for maybe 15 minutes. Just my opinion, experts may disagree.
You have to find the right size cups.
https://www.noogleberry.com/collections/breast-enlargement-products
Many CDs wear wigs, breast forms, hip pads, corsets and such, which are obviously temporary but I could never feel good about wearing them.
Hell, I don't know why it bothered me... many women wear all of things, every day.
Shaving or epilating my body was always important to me. Shaving is temporary. Epilating with laser or "Epilady" can yield permanent results.
I think this definitely adds to a feeling of femininity.
I agree that if you take herbs at a high enough dose to feminize your body, your brain is affected.
You will start feeling more feminine and desiring more and more change.
At least, this is my experience.
I always feel awkward giving advice because there are so many variables and I don't know if I am on the right track.