I would first have my water tested to determine what was causing the staining. Once you know what is in the water, you can install a whole house filter system focused on addressing the findings in the water. Are you sure it is the water? It could also be something in the products used to build the shower. What types of walls do you currently have?

For temperature regulation, I love technology but I am sticking with a simple Thermostatic valve in my shower. The digital ones seem to be well liked but I don't know much about them. Are you just looking for the valve and trim for the temperature and volume controls or are you rebuilding the shower?

Thanks for the response!

I'm looking to do some major renovations, like move the shower/tub upstairs, if possible.

I currently don't even have a thermostatic valve. I have two separate dials for cold and hot. It's annoying, in the morning, having to run the water for a while and adjust to get a stable temperature, then adjust as I shower.

Right now I'm gathering information, like what options are available, pros/cons for all the questions I have.

The yellow spots occur on the ceiling. I'll get my water tested. Though I'm pretty sure it's just the hot water. I would like to have all water coming into my co-op unit filtered.

https://drive.google.com/file/d/16nI9ljBjiSkrtrgfq6pUFaI4G93sGe-6IA/view?usp=sharing

That is interesting. It does not look like mold so all I can think it is some sort of reaction. Get your water testing and then specify a filtration system for the incoming water supply.

I used both Grohe and Hansgrohe Thermostatic valves in my bathrooms. They are equally good in my opinion. Take a look at their website and pick a style you like.

Moving the shower and tub will not be easy if there is no existing bathroom upstairs. I would reach out to a plumber to figure out if you can add the bathroom in another location.

Could it be a leak from upstairs? You can learn more about the water chemistry by going to NYC.gov and checking NYCDEP water quality reports.