Overheating problem

I am having issues with my car recently.
Sometimes while going uphill or just waiting at a signal the temperature starts to rise and most of the time temperature goes back to normal after the double fan start, but sometimes it shoots up to overheat point I immediately stop the vehicle and when I restart after like five minutes it goes back to normal.
The problem is I have to move around its part of my job so recently it got frequent like temperature goes up I stop the car after five minutes restart and we are good to go same thing happens after fifteen to thirty minutes of driving.
Kindly note that I only got hot engine sign three or four times and I stopped immediately but normally if the needle of the temperature gauge is one point below the overheat I stop immediately!

I consulted someone they said it is thermostat valve and thermostat itself, but I suspect there is something else because the fans turn on, but sometimes the temperature rises and sometimes it goes to normal. Please help before something serious and expensive repair comes on my head.