neighborhood across from mine, owners have a very good looking light blue 230 convertible with a dark blue top thats parked outside. and after all these years the top looks fantastic and I don't think they're using any high-end or serious hand washing routine.
just wanted to suggest that you don't need to get too worried about top degradation.
I buy stuff from carcarespecialties, great customer service. P21 auto wash has a very nice car wash soap that seems like it would be excellent for a BMW soft top.
https://www.p21s.com/portfolio/p21s-...oning-shampoo/