Boost pressure is already monitored by the ECU and is available through the OBD interface.
Those of us who have fitted a Tilix valve (like me) will have a hose coming off the turbo's output pipe that could be tapped into in order to fit an independent gauge, but you could just throw a bluetooth ELM327 OBD2 adapter in and get the info (and a bunch of other stuff) direct without much effort at all!
Hmmm anyone know the possibility of sending obd info to the head unit screen via bluetooth as opposed to phone or tablet? Might see if I can "hack" my kenwood
Depends on the head unit. I bought a Pumpkin Android head unit (that is NOT an endorsement - see below). Using the app "Torque" I have all the data available on my head unit whenever I want.
Pumpkin head unit issue: just the one. While it has bluetooth and I can use my phone, they crippled the BT audio so I can't stream music from my phone to my head unit. They do supply an additional component that restores the functionality. I won't ever do that again.