Marinda. Get your plumber to check the RMC technical Manual or contact me on my email with regards to a pressure reduction valve set to slightly below the lower pressure switch setting, this will give you a constant pressure throughout the house and from the hot water system. this valve should be fitted to the incoming cold water to the building so that you have equal pressures to your shower.
alternativly check out a constant pressure system price yourself. The price of having a decent shower may end up to be similar anyhow.
Bob