DSG 140 not getting to 90 degrees

[Dee4Life]

Multiple threads on this and I've read them all. Quick fix is the replacement of the inline thermostat to DSG which has been done to no effect. From what I've read the next steps are to replace another thermostat (may be two more?)-I've read this is a hassle to do can anyone advise? I.e. Where is it?

Also suggested is changing the Cooling Temp Sensor- again how easy is this to do?

Any advice on price of the above welcome.

Really annoying in this cold weather.