There are many options in maternity shirts from Old Navy. There are tanks for layering, nursing, or for use when the weather is warm. There are also long sleeve and short sleeve maternity T-shirts in many stylish colors and patterns. For those looking for a special occasion outfit, or something that can be worn to work, there are also tops that can be worn with dress pants or skirts.
I worked for Reitman's for over 9 years, moving to all branches, eventually being moved to thyme because they said it was the only store I would be able to advance in. After working there for a year and a half I was told that they were just going to hire from the outside instead because it wasn't fair that I might play favorites. While I enjoyed the time spent there with the people I worked with it wasn't a career sadly.
The advantages of under the bump are that they aren't so bulky under tops and to combat exposure or to allow you to wear a shorter top you can always wear a belly band or long vest top under your top top. Under the bump tend to work better for skinny, stretchy style jeans as the stretch in the denim will hold the jeans on your leg as supposed to having to rely on the waist band only.