sometimes overheating can be caused by head gasket failure, you can get a decent garage to check this for you though.
The coolant sensor can be a bit tricky to do as if I remember it is sort of under the inlet manifold.
Also check your coolant levels are they okay? If your car is a classic the radiator end caps are prone to cracking and usually you cannot see this when the engine is not under presure, also check the top rad hose and the bottom rad hose to see if they have got splits in them as again with age they can become brittle and spew out coolant under pressure.
The stat is easy to change, I have had one stick closed which caused me overheating issues and also a split radiator and top hose. You will have to remove the bottom hose and it is fitted in a houseing on the engine side, if i remember the housing is held in place with 3 bolts (I think 10mm head), be careful removing these though as with age they can shear off. When I have changed my stat I put new bolts in place. Once removed you could check your stat by dropping it in a jug of boiling water to see if it opens or not.