You made the right decision: Paris, no question. Rome will be unbearably hot in July, and there will be so many tourists there you'll spend most of your time waiting in queues dying of heat exhaustion. Go to Rome in the very early summer or Autumn. Paris is not as 'exotic' as Rome and perhaps not as interesting (for my tastes anyway), but it will be cooler, and it's slightly less crowded what with its boulevardes and grandes places.
Also, going to other parts of Italy is a good idea: Rome is nice but it's got a very individual identity, it's not the same as going to other parts of Italy. Go to Florence, Venice and Verona, or Sicily if you're feeling more adventurous, as well as Rome.