[murphyv310]

Hi and welcome to the club.
It is unlikely to be the engine as a unit.
Do you have the full list of what was done on the both recent "repairs"? What year is the car? The reason I am asking is you say it has a new thermostat. Later cars have what is known as a PRT thermostat fitted, it has three pipes and lives along the lower edge of the radiator. Often a garage will fit a standard thermostat where they were originally fitted on the early production cars effectively having two thermostats in the cooling circuit. Some find it works OK but many have the overheating issues you have. Time to get it confirmed if you can.
The other issue is bleeding it should be done as MGR suggests, although vacuum filling should be fine.
Another simple thing is the condition of the coolant expansion cap, any doubt fit a new one not a cheap copy, the O rings in the grooves of the cap can get flattened and cause pressure drop and leak, sometimes new O rings are all that is needed.
The trader DMGRS here can supply a new cap and O rings.
Good luck and don't give up.