First, I must disclose that I am retailer of harnesses and I am a certified Buddy Belt fan-atic.
Most harnesses will fit over clothing, but I love the Buddy Belt because it is so easy and fast to put on and take off. Depending on where your pup fits in the size range, there should be enough room to fit over clothes because the BB is adjustable. There are cases where pups fit at the top range of a BB size, and there isn't room left for clothes, while the next BB size is too big.
I also love that the BB doesn't come anywhere near the neck and it doesn't have to go over the head.