Measuring the chamber temperature of the engine in a hot fire test

[SamD]

Hello,
I am trying to design an instrumentation system to measure the temperature and pressure readings in a model rocket engine. I am stuck on how to measure the temperature in the chamber.
I am planning to use thermocouples to to measure temperature. But the idea I get online is that I can measure the wall temperature readings and thermocouples cannot measure the temperature inside the chamber too.
So can anyone suggest how to get the chamber temperature?