The "right" way to do this is a thermostatic mixing valve at the water heater output. This lets you keep the tank at 150°F (or whatever) but the output gets mixed down to 120°F (or whatever). It also gives you an effectively-larger tank which can be very useful in certain cases.

Of course, you might say, why not put the thermostatic mixing valve at or in the shower, which also works pretty well!