I went from a 135 coupe to an E90 M3 purely because I have 3 primary school kids. Loading them in and out and strapping in the seat belts became a pain as I had to climb into the car. It's not fun when it's raining either. The longer doors of a coupe make ingress/egress harder in tight carparks. Don't forget your newborn will be rear facing for quite a while esp under new seatbelt laws. We don't have ISOFIX here so you also have to lift the baby over and thru the restraining belt.
Also, coupes with baby seats dont look cool.
2012 BMW F10 520d M-Sport
2010 BMW E70 X5 xdrive40d