Was looking for my post that asked the same question. Basically you can purchase the GROM bluetooth adapter like I did or save up a grand or more to do custom work. Nobody makes s*** for our cars and lots of the stereo places I called didn't even wanna touch it because of how finicky our NAV is apparently

. As I understand it, all the electronics that run through the dash connect to the NAV unit which is notorious for having issues with installs.
The GROM unit is ok, not great (costs about $200, did the install for $75). I have to turn my phone and stereo unit up almost all the way to get to the volume I want. Sometimes the bluetooth doesn't want to connect right away either and takes 5+ tries. Is it better than nothing? Yes. Is the quality top notch? No. But it's still better than spending thousands of dollars to completely redo your dash. (Note: 9/10 places I called about the GROM unit never even heard of it. Some were adamant about anything working for my car, 06 M45)
Good Luck