Yeah you can DIY it if you buy the boot module, I think as you have the 6FL USB interface then it's pretty simple if you don't mind playing with wires. If you have a spare £600 (cheaper than BMW will quote you to install the OEM version, circa £1000) then look into Mobridge or Fiscon, like-OE functionality with full radio and steering wheel control
I do however have the BT Phone Prep in mine as standard and I rate it highly. The voice recognition can be a ball ache at times but it saves you taking your hands off of the wheel. I'd never have a car without this or NAV professional again.