You can get a shutoff valve made for shower hoses at Lowes, Menards, Home Depot, etc. Fairly cheap. I bought one but didn't like the extra heft because I thought it would keep the shower head from staying in place during travel. Obviously, I could just lay it down in the tub.
The general experience is that with a complete shut off, when you turn it back on the temperature will be way off for a while. So most designs allow a trickle. I think the one I bought was a complete shut off but I can't say if the temperature change was a problem.
