Hi my setup is like this:
Becker CR-22 Tape deck (I have some 90's mixtapes in the car 8) )
Becker AUX wire. This plugs in where the CD changer normally plugs in. You then enable AUX in the secret menu of the Becker. You ahve to ditch the CD changer.
£2
https://www.ebay.co.uk/itm/3-5mm-AU...sat-B5-Bora-Becker-Blaupunkt-Hoc/191476922546
Dual USB power supply - supply from ignition switched on the headunit wiring. One USB powers the bluetooth adapter, the other can charge the phone.
£2.30
https://www.ebay.co.uk/itm/12V-to-5...=item239fdce86c:g:TmAAAOSwZola6Yn0:rk:21:pf:0
Besign BK01 Bluetooth 4.1 car kit. I notice they do a newer BK03 version now. This includes a ground loop isolator which I needed to cut noise.
£20
https://www.amazon.co.uk/Besign-BK01-Bluetooth-Hands-Free-Streaming/dp/B01MSUWCZ0/
https://www.amazon.co.uk/Besign-Bluetooth-Hands-Free-Streaming-Wireless/dp/B073S6KR2G
I put the phone on a ball mount like this stuck at the front of one of the centre console trays (mat removed)
https://www.amazon.co.uk/Anker-Universal-Magnetic-Mount-Ultra-Compact/dp/B0716PJK33
You just plug it all together, I routed the circular Besign bluetooth adapter by just tucking the wire behind the A pillar cover, and used my own double sided foam tape to secure it near the top of the A pillar as the supplied was rubbish.
Calls are good quality (considering its a noisy car). You can answer the call with the button on the unit or from phone screen. To make a call though you have to use the phone screen - but I never do that when driving.
Music quality is brill. I usually play BBC iPlayer radio catchup, or podcats, Spotify / mp3s on my phone. You can skip tracks with the buttons on the unit.
The only issue is when you are listening to the headunit radio, or a tape and a call comes in. You have to switch to AUX - the listening is not interrupted by the call.
Had this setup for a year or 2 now and happy with it as it retains the OEM looks and I actually rather like the SQ from the Becker.
I don't tend to interact with it when driving really, just set something playing and I'm not someone who is always on the phone either. I tend to leave the phone in a pocket rather than on the mount as I don't interact with it.
I plasti-dipped my sticky volume and the other becker knob. I also replaced the ancient nokia speakers with some new pioneers.