There's plenty of old-school single DIN devices that have bluetooth in them. You'll usually find they have a radio and other junk (e.g. mp3 over usb) but most

There's plenty of old-school single DIN devices that have bluetooth in them. You'll usually find they have a radio and other junk (e.g. mp3 over usb) but most are fairly simple and it shouldn't be hard to find one that stays in bluetooth mode all the time.