Which shower valve do I need?
Any one of a number main line manufacturers' valves will work in your situation.  You have what is called simply an in-wall, single handle tub and shower valve.  Some soldering will however be required. You could use a pex pipe type valve or even a iron pipe threaded valve that will accept either galvanized pipe or CPVC. However you are still left with adapting to the existing copper pipe.  Good Luck.