For those wondering why, look at his location.
"ooooh, I get it"
It's a tough situation there. When sitting at a traffic light, you're above ultra-hot pavement which is radiating a ton of heat, and surrounded by other vehicles radiating more heat and trapping the air (mini heat island effect).
You don't want to lower the operating temperature of the engine, you just need the engine to be able to stay at it's proper temperature no matter what. If the foot wells are getting hot, but the engine temperature is not going past normal, then there's nothing wrong. If the engine temperature IS going above normal in these circumstances, then there could be a technical problem, or it just can't keep up with the intense ambient heat.
If the official weather actually is reaching 55C there, then you could easily find your Jeep sitting in pockets of 65-75C ambient temperature at times, or higher. Here in California just a few weeks ago, I took a picture of the Wrangler's rear view mirror thermometer reading 138F (59C) while sitting in a fast food drive through, surrounded by concrete and other cars. The official temp was 101F (38C).
This leaves very little room (just 15-25C) between the air temp and the desired engine temp. This means the cooling system itself is having to work very hard to keep the engine from overheating. There's no room to lower the temp of the engine any further. The only thing a different thermostat will do is let the coolant flow out into the radiator at a lower temperature. This does nothing if the temperature is already high enough for the thermostat to be always open - which it probably will be in your case.
The only things you can do to increase the engine's cooling capacity are:
1) More airflow over both the engine and radiator. This means more powerful fans when not moving, or more of them if possible.
2) More surface area for the the heat to dissipate. This means a larger radiator or more radiators.
3) Ensure the air flowing over the engine and radiator(s) is coming from outside the vehicle. This can be hard, and won't always help when sitting still, as the post-radiator air begins to fill the area around and under the engine bay. Also, sometimes making more vents can worsen airflow and increase temperatures.
If you don't have the factory cooling options for the engine and transmission (I suspect they're standard over there?), then have the dealer install them for you.
Is the engine ever actually overheating, or is the needle ever approaching the overheating range on the gage? If not, and the only symptom is the heat entering the footwell and the AC getting weaker, then you do not need to worry about the engine's temperature. These things are caused by the build up of warm air in the engine bay and under the car when sitting still. In fact, forcing the engine to a lower internal temperature with a thermostat would increase the amount of heat in the engine bay and thus worsen the footwell and AC "problems".
Have you had other vehicles there which did not exhibit any of these symptoms?
For the A/C, you could have an A/C specialist increase its capability. Yes, they can do this. I've heard stories of HVAC technicians tweaking their service trucks to blow air so cold that the dash vents get frost on them.