2006 A4 Cab RNS-E without Bose - How to add USB / AUX

Hi can anyone advise how to do this, is there an out fo the box kit i can buy, ir should I just replace the headunit with another ?

I have the CD changer in the glove box, Happy to lose this i have an old ipod floating about somewhere, i could use or ideally just bluetooth stream from the phone or plug in a USB stick?

Seems to be lots of options about from £10 cables on ebay to replacement headunits from xtrons ? any advise on whats the best way to go.

Thanks

DJT