There are basically 3 types of valves.
The first is the one you have... the old on/off with some basic adjustment. A little shocking when others use water.
The second and probably most common is the Pressure Balanced which adjusts hot and cold pressures to match with water usage and the resulting pressure fluctuations. Cost on these is about $100 on up and they will maintain +- 3 Degrees F approx.
The Last and The best is the Thermostatic this probably starts in price in the high $200 range on up. This physically measures the water temp and maintains it to about +- 1 Degree F.