There are a lot of threads about water filters, if you do a search. The only showerhead water softener
I recall reading about was something called a ShowerStick but most of the threads are about water filters
(chlorine). I prefer to use a shower filter and an occasional sulfate poo, while others prefer to use a clarifying conditioner or low poo (sulfate free) with EDTA (or other chelating ingredient) to help remove the build up from hard water.
ETA: Thanks for posting the highlights of your conversation with Mary Pat. I hope the coconut curlada continues to work well for you!