Like Karren, I've never bought anything but "off the rack" corsets, Bella. I have 6 or 7. And, have found that over time, often the CORSETS will actually form to MY FIGURE!
My size is similar to yours. I weight 150, too. Many larger girls like custom corsets. But, start with an inexpensive one and see how well u like it. I also have a Glamour Boutique corset. Simple, basic, well made, economical. Start with a size 26 or 25 if they make it. Some companies only make even sizes!