Chevrolet Cavalier 2000

Hi

My engine temperature gauge is around 100 deg when i'm stuck in the traffic for a long time but when i'm on open road it's just below 90. I'm thinking my thermostat opens at 98 deg, so I want to put one that has lower temperature rating. If I do this will it affect the performance of the car or in other words is this a safe to do. Also I checked the level of my antifreeze it seems to be fine. Thanks for the help in advance.