My car keeps overheating. We've replaced the thermostat?

Hello,

An engine can overheat due to a bad water pump, inoperative cooling fan, clog in the cooling system, stuck closed thermostat. It can also overheat due to being low on coolant.

Here is a helpful guide:

https://www.2carpros.com/articles/engine-overheating-or-running-hot

Since you have already replaced the thermostat and check the radiator and coolant level. The next item to check would be the radiator fan.
Does the fan come on when the engine is at operating temperature?

https://www.2carpros.com/articles/how-an-electric-cooling-fan-works

In operative cooling fan can be due to a bad relay, wiring issue or a bad fan motor.
Check the relay first, it is located in the fuse box under the hood.

Another possibility is a bad water pump, which is unable to circulate the coolant properly through the engine.

https://www.2carpros.com/articles/water-pump-replacement

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.