My problem has been that our shower head has a valve on it, which I want, but they drizzle, when closed, which allows the hose to fill with cold water.
What I have done is go to Tractor Supply and in their farm/field sprayer area they have 1/2" National Pipe Tapper, NPT, to threaded Garden Hose fittings. This would be, female pipe to male garden hose, and female garden hose to male pipe.
Take the shower head off the hose, Put the adaptors on the hose and head then put a garden hose valve on the hose then the head on the hose valve.
Now the when you turn the garden hose valve off, it will not drizzle, and the water temperature will hardly change.