Serious advice:
My S/o has been corset trained (off and on), and has been pulled in as much as 6 inches from her "natural" waist for extended (i.e. a weekend) time. For anything over 4 inches, you should have a custom one made, and consider a "tube" for under it. If you are going to seriously try to change the shape of your body, a canvas, "practical corset" may be something you should look into for day to day wear, with fancy ones for special occasions. Expect to have a pattern made (possibly more than one if you go for different cuts, i.e. over the hip, under-bust, or other combinations), then for your other custom corsets to be made from that pattern. The shop I've used for about 8 years charges about $400 for your first corset (cloth) that included making the pattern to the person's measurements, and then $200-1000 (depending on material, complexity, built in bondage straps or rings, etc) for your further. If you are a regular customer, they'll usually do a new pattern for you for free (necessary if you gain or loose more than 8 lbs or so). "Dark Garden" in San Francisco has been where I usually have had my wife/slave's corsets made, and we've been very happy with their products. They are on the web.
If you are just looking for something that shapes a little and makes you look nice, then Versatile fashions will probably be a good place to start, and for MUCH less money. It's the difference between a piece of lingerie and a fetish/training article.
And, my dear Trolling Lady, somehow I doubt that you require an "investment" in fishnets and heels. I would think that you already had them...if not, the gentlemen in your life have obviously not been taking care of you properly. My S/o has a monthly lingerie budget that she is expected to spend.
-SB