Having your boobs done isn't going to give you a cleavage. All a boob job does is enlarge them not bring them closer together. Only a push up bra or tit tape will do that (or tight clothing).
When I had my first set done back in 97, the surgeon asked me what size I wanted to go up to. I was a 30B (I was only a size 6 on the top, and a 12 on the bottom, so finding dresses and suits to fit me was a nightmare). I asked to go up to a C cup, as I didn't want huge boobs. The surgeon (although he was happy to give me a C cup), recommended I go for a D cup. He gave me his reasons for this, which were, going from a B to a C wouldn't make a great deal of difference, and that it wouldn't be money well spent. He showed me a C cup implant, which was a very similar size to what I was already, he then showed me a D and a DD implant, and asked me what I imagined my boobs to be like after the op. What I realised then, was that a DD would probably be best suited to me. So my first set were a DD, and they were a nice handful. Not too big, not too small. My current ones are a G cup, but that's another story, for another time.
Although you say you'd like to go from a D to a DD (if you do decide to get them done), if the surgeon is a good one, then s/he will show you the different sizes and you may opt for a bigger size if you have an idea of what you want your boobs to look like post op.
I cannot comment on whether it is good for business, as I had mine done many years before I started as a sex worker, but as many others have advised, do this for you not for your business. You might decide to move out of the sex industry in a years time, and you would have spent all that money on something you didn't really want.
