Thermostats generally aren't the problem, though many are sold to customers who are then sold other stuff, the the supposedly "needed". A bad radiator cap will also cause overheating especially if the electric fan is working.

If you end up having the system flushed, be mindfull that flushing sometimes kills off the last of what was holding yer radiator together so be prepared for the guiy to come to you and tell you that you need a new radiator.

Good luck,

Bobert