

It’s reasonably common for showers to have a mixing valve and a flow rate valve on separate handles. That accomplishes what you want. You just have to remember which is which and only use the flow rate valve to turn on and off.
More importantly, hot water circulation systems should be more common. It’s the waiting for the cold water in the line to flush out that really makes setting temperature a hassle.




The solution to that is for a third return line to be run during a new build or remodel, but that’s definitely not a weekend project for most homes.