Sorry, I'm in the U.S. so I can't recommend an installer, but having just done it myself, I can give you this advice if you decide to try to tackle the job:
1) Make sure you buy all the install parts before you start. You will need the steering wheel adapter module, a wiring harness adapter made for your car, and probably a bracket/faceplate kit.
2) Search on line for as much information as possible about how to install everything. You should be able to find detailed info on how to disassemble the dash. You may should also try to get details on how the current car radio is wired. When I did mine, I found a drawing of my car's wiring harness that detailed each pin and what each wire was for - that helped me get the right wires connected. It also revealed that the matching connector I got to connect to the Pioneer unit was missing the wires for the steering wheel controls. That made the install more complicated - although I still managed to do it. Also, if you buy a steering wheel control module, you'll want to visit the manufacture's web site to make sure they provide detailed instructions tailored for your Golf.
If the wiring harness you purchase has all the right pins and wires, you should be able to sit down at your desk or kitchen table and make all the connections before you even start to disassemble the car.
Finally - give yourself plenty of time. If everything goes smoothly, I could see completing the work in 3-4 hours. Mine did not go smoothly, and I think is spent 8-12 hours total. That was a big investment of time, but I saved $150 or more on install costs, and now I know how everything is hooked up, so if any changes or repairs are required, there's a good chance I can do them.