Hi Paul, if you buy the VAG G12 Plus coolant you can mix up to 3 parts coolant to 2 parts water and it will protect down to -52.
It's pretty high spec stuff and was specifically designed to prevent head gasket failure in VAG engines.
You will need to flush all of the old coolant out of the engine first, preferably with a chemical cleaner and the thermostat out, as green coolant does not mix with the lilac G12+.