Todd77. With any pressure pump that you have described you will have a upper & lower pressure switch setting, bloody annoying if standing in a shower.
With modern pumps, you can get a constant pressure system where the pump will controll the flow at a predetermined pressure.
Alternativly you may wish to install a pressure reduction valve adjustable to whatever pressure below the lower pressure switch setting. The advantage here is you have a constant pressure without the pressure switch fluctuations.