I went along to my local Peugeot dealership who were extremely helpful!
One of the sales people took me along to a 2019 108 which had a display head unit with 3 buttons. I plugged in my 'non-mirror link compatible' android phone and straight away my phone and the display started to communicate with each other. My phone asked me to confirm a few privacy things like you do when you first use a new app and hey-presto it all worked! I tried Google maps - that worked! and I tried the BBC Sounds app as means of a test as well and that also worked! - Perfect!
So, now the dealership are going to get me a price to supply a new head unit and also to fit it (once the parts department opens Monday morning). But I will try and find a second hand one to fit myself.
Bottom line is that as long as your Android phone is running Android 5.0 (Lollipop) and higher it should work with Android Auto and the new 3 button display.