Take a look at two Subaru's - the Forrester and the Outback. AWD, heated seats, a lot of safety features but not all you are suggesting to keep it in the price range, they will meet your fuel consumption needs and are all around long lasting, great vehicles. To get Nav in either, you will exceed your price threshold so good on Garmin and smartphones. Also, with Bluetooth you can download Google Maps on your phone and turn by turn directions will transfer to your car speakers.
If onlyl Passat were selling a wagon (I had one with AWD). That would more than solve the back seat room issue for your son. If you could find a used one with low miles and in good condition, you would have to consider it. Yes, Maintenance cost will be a little higher for the German mantra, what a comfortable and safe vehcile on the road. Don't rule it out. The Jetta Sportwagon TDi will exceed 40 mph but back seat is tight.
Good luck with your search.