Not sure what's readily available on the other side of the pond, but I put in a Pioneer headunit with bluetooth, used the Metra dash kit, and I think I used the PAC steering wheel interface. Total cost was about $250 USD and a few hours of labor, but the sound quality improved indescribably - even with stock speakers(I replaced them eventually too).
Now I just switch to bluetooth audio on the radio, and my phone automatically starts where it left off. The audio controls can skip tracks even on Pandora, Digitally Imported, Slacker, etc. streaming services. Works well with Android, especially.
If you look around I made a guide on wiring the steering wheel audio interface - you'll need a second dash harness to salvage pins/wires out of to do it right, but it's more reliable than T-taps/vampire taps.