My thoughts are:

I know how hard it is for busty/curvey/etc. women to buy jackets.
Maybe look for non-traditional styles such as trapeze as well. Sometimes they fit us differently than the loose intention and then they can work.

Other options- cardigans! A nice structured sweater can take place of jacket.
Dresses - then you don't need a jacket.
Skirts with tops. When you wear a skirt and a nice shoe and accessorize the outfit, people assume it is dressed up compared to slacks with same outfit.

Mix and match the basic jackets you are finding and go ahead and wear a few times a week (just change bottoms, base layers and accessories).

Hope that helps - I can't wait to see what everyone else thinks.

I like all of Chris' suggestions. My first thought was that you could probably wear that black jacket as much as 3-4 times a week without anyone noticing it's the same jacket! I.e.,

1) With matching black pants

2) With camel or white dress slacks

3) Over a sheath dress

4) With a pencil skirt

Four very different looks with the same jacket!

But you may get bored with that!

I think a sheath dress with a nice cardigan would be a great alternative. What about a pencil skirt with a vest (see Maya's recent interview outfit photo)?

Are you in the northern hemisphere? If so, then that makes it a little easier: I should think during the summer months a jacket is not a strict requirement? What does the dress code say, specifically?

Wonderful suggestions.

Where do you currently shop, aurora?

Aurora, you and I are in the same size bracket, so I definitely hear what you're saying. But don't worry, we have lots of options, many of which have been touched on here. One stroke of luck is that a jacket isn't strictly necessary to pull off the professional look (though I absolutely think you should have a couple in your wardrobe). Dressier tops and bottoms, paired with appropriate heels, will get you far in an environment like that. Make sure to have a decent selection of flattering, dressy bottoms as well as a variety of woven tops and camis. These pieces will allow you to mix and match outfits on a more limited budget while still looking very polished. Angie advocates layered looks and that would certainly work in a more formal office setting when done right. That, of course, means ensuring everything fits just so. Here's another vote for dresses and cardigans, too. Dresses and skirts step up your formal factor without even trying! Heels and jewelry will also give the right finishing touches. For the price of a well-tailored jacket, you should be able to pick up a few of these pieces and get yourself started.

Thank you all for the help, I've printed this out and every payday I'm going to buy an item to keep building my wardrobe.
I've gotten a few items at Talbot's, Nordstrom’s and I just found out that Ann Taylor has size 16-18 on line (not sure about store). I live in Pittsburgh, PA and work in a financial investment firm that is really going back to professional appearance. Since a recent weightloss I did purchase some clothing before the roll out of the dress code so, I do have sweater sets (several) and trousers from wide leg with cuffs to a slim leg. I like the accessory idea maybe get some scarves. What is the best way to wear? I've seen a few ideas on here.
Again, thank you for the idea...it is sometimes so overwhelming for me to go shop.

Aurora, you might want to especially look at Bellacville's pictures in the What I Wore section. She often wears skirts instead of pants, but she has some great cardi looks. For more cardi inspiration, see Shiny's pictures.

A sweater set can get lots of mileage by breaking up the pieces and wearing them separately. The shell, whether sleeveless or short-sleeved can be worn over top a button down shirt like one would wear a vest. Scarves, belts, and a couple great necklaces (esp a long strand of pearls - real or fake) can change the look completely to help maximize your wardrobe options without spending a fortune.

I also wear business attire at work, and I am finding this summer that dresses are my main go-to outfit. The trick is finding work ones instead of party or casual, but it's not as hard as it seems. I've had luck at ATL, Target, and Ann Taylor Outlet, to name a few places -- and ATO and Target do carry 16s.

I also wear tons of cardigans -- with the dresses, with skirts, with pants, etc. I actually don't even have to wear a jacket most of the time, and I look dressier than most of my counterparts!