Thermostatic mixer showers are very common (in the UK at least) and are very affordable (sub $100) and as reliable as your hot water supply. My understanding is

Thermostatic mixer showers are very common (in the UK at least) and are very affordable (sub $100) and as reliable as your hot water supply. My understanding is that water pressure is much harder to control for; there's so many variables that you just can't do anything about, and without installing a giant tank and a pump if your pressure is low it's always going to be low.