Tara, I use the part-skim mozzarella all the time, it's better than using the whole milk mozzarella. As for only having the Mexican cheese blend available in reduced-fat, I would just use that in anything I want cheese for.
Do you use cream cheese? If so, buy the Neufchatel cream cheese since it has 1/3 less fat than regular. Lowfat or fat-free cream cheese isn't always available, and I think neufchatel tastes better, anyway.