Quick update....
I had to bite the bullet and buy the radio. Seriously doing my head in not being able to multitask.
I've found, whilst streaming music, and having Google Maps navigate me, and receiving calls, and messages from one of a million different apps - the OEM system just doesn't handle it all well, and needs me to use the handset whilst driving - which isn't going to happen in the UK.
I've become accustomed to having screen handoff, and the stereo unit sharing the processing, meaning, I can answer messages by voice, have the GPS running on screen, and take calls, whilst streaming music.
I've ordered it from the manufacturer at $150 ish and it's coming from China.
Let's see if this works - or if the car spontaneously combusts! Hopefully it arrives before my impending road trip!