You need powdered surfactants such as SLSa, SCI (about 70%) waxy emulsifier (say BTMS), you can use stearic acid to make it harder (but it will be draggy). And you absolutely need sodium lactate. It makes bars harder.
I dismantled the old bathroom with the help of my brother; he understands more than me how all this plumbing is arranged. I could advise you something about the stage of repair when you are already installing new plumbing in your bathroom. I studied the shower stall market for a long time and installed plumbing fixtures in the house from https://gethai.com/. I like their “eco-friendly” approach to their products. I wish I had seen the photo in one of the comments above earlier; I liked this idea with wine haha. I wish you good luck in solving your problem, and I think you will succeed