I sadly have always had an apple shape (big tum), irrespective of dress size. I’ve always preferred trousers/smart separates than dresses, which I feel make me look frumpy (due to my ever present tum). I am envious of your hourglass.
Right now I’m size 16/18. My go-to for the office includes slim cut/straight leg/cigarette style trousers. Wide legged and high waisted are a big no no for me. My ankles are one of my slimmest parts, I need to highlight them 🤣. Trousers in wool or a tweed like fabric, with leather boots or sexy heels, can look quite sharp.
On top I would either go for a cashmere jumper or a cute little blazer/boucle type jacket, depending on how formal I wanted to look. The blazer would either be cropped or 3/4 sleeves, with a skimming top/blouse underneath.
Sometimes I like to mix it up and wear a pencil skirt, with a skimming top/blouse to cover my tum. The tv character, Rachel Zane in Suits, does this look beautifully (though I don’t have her figure & she doesn’t have a tum to hide). But I do get more compliments on the rare occasion I wear a pencil skirt.
Basically I like to wear fitted/slim cut tailored type pieces everywhere except my tum, which I try and disguise with a skimming top.
Smart separates would work in a corporate environment and if in a restricted colour palette, all pieces could go together.
If dressing for a promotion, it’s not just about the clothes. Think about the whole look, hair, accessories, shoes etc. Treat yourself to a couple of beautiful pieces, like a well cut coat, beautiful bag etc. The most important thing is to feel confident in whatever you’re wearing.
You could try going to a department store, spend some time trying different trouser cuts/styles. I spent years avoiding skinny jeans because of my size, yet it’s probably one of the most flattering cuts on me, as it helped show the slimmest part of me & didn’t add bulk to my frame.
Have fun with it. Good luck!