Thermostat

[jasst]

I have a 2006 2.0FSI 147kw version, and have come to the conclusion that the thermostat needs replacing as on a cold day, temp gauge doesn't go above 70, Have looked on several sites such as autodoc (never used before) and loads of different ones are listed, dif temps, dif shapes etc, so how the hell do I know which is the right one?