Hi,
First, congrats that you`re going to have a baby.
Generally speaking, if you`re pregnant, the best time to travel is between 18-24 weeks (second trimester). During that time, the morning sickness should go away and your belly will not be too big . If you are healthy and exercise reguarly, it is actually okay to travel far. I personally went to Europe with my husband while I was 4 1/2 month pregnant. We went to Paris, Prague and Rome for 12 days and I planned the entire trip myself. We did not join the tour, which means we walked a lot and lifted luggages ourselves (of course, my husband helped me a lot =p) Just think of this way, you won`t be able to travel to places you`d like to go once you have a baby, if you plan well, just go. Joining a tour might be a better if you have any safty concern. If your fly hours are long, just be sure to walk around and drink plenty of water, you`ll be fine. Enjoy while you can!