Toning up the Bod

I am interested in finding a good exercise plan to help tone my body a little bit. I am comfortable with my size, I just want more muscle and definition. However, my husband and I are trying to conceive so I want a program that will be safe for when I get pregnant. I plan on talking to my doctor soon about what she suggests but I was wondering if anyone knows if specific exercises are better than others in my situation. Or if I start now, then when I get pregnant I can just decrease the strength...