Are you sure the car is actually overheating or are you just going by the gauge?

I don't know that the low temp thermostat is the route to go. If you think about it when you have a low temperature thermostat it calls for an exchange of coolant more often. The coolant that is returned to the radiator does not have long to cool before the thermostat is calling for an exchange again.

I assume you have physically cleaned the radiator by removing it and using a garden hose to flush (from the back side forward) all the grass clippings, cat hair and grit that it collects. Hold it up to a good light source and double check it. Straighten any bent cooling fins. While the radiator is out flush the AC condensor the same way. Is the radiator showing good flow?

Randy