I have tended to be a 16-18, also with very large breasts and an annoying belly. I'm slowly losing weight as well but it's not super quick. I have, admittedly over a period of years, found that a surprisingly large proportion of my wardrobe is made up of purchases from those stylist boxes you can order - I originally got from Stitchfix and when they shut down, I started getting from Outfittery, I would highly recommend you consider ordering 1 box, telling them exactly what you need/ don't need and see what you get. The big challenge is that it can get expensive doing all at once. I tend to keep 1-3 items in a box, and only get a box every 3-4 months, but it might be worth ordering 1 box, aim to keep more, then order another box shortly after.
Things they've sent me (or in some cases, that I've bought) and that I wear a lot for a similar sounding job/role/company in the City include:
A couple of different pairs of wide legged trousers with elasticated waists! I wear these with either plain v-necked t-shirts over which I can put a jacket if necessary, or with more structured/ patterned blouses/tops that don't need a jacket. I personally like a jacket/plain t-shirt combination if I'm meeting externals etc but just in the office I like without the jacket.
smart tailored trousers or jeans (black jeans/denim only). I wear these with a selection of very soft v-necked shirts they've sent me over the years. I find that a regular shirt often lands up being too boxy, but for whatever reason, Outfittery/Stitchfix have successfully sent me a few that are suitably soft that they fall nicely. I have previously had success buying shirts like this in person from places like White Stuff/Fat Face. I usually wear these tpes of trousers with a belt and I slightly tuck in the shirt at the front/waist. That works for my body shape although was harder when my stomach protruded more (I still carry weight there, but my breasts definitely stick out MORE now so at least I don't look 6 months pregnant).
I have had a couple of dresses I've bought over the years. True cross body type dresses often don't go over my breasts but they send me some or I've bought a couple that look like they're wrap dresses, but aren't really. Then I usually wear a small vest to manage the low cut nature or sometimes I can pin it.
ETA: One thing I've found is that when I buy from these boxes, it can be a bit more expensive, but I really do seem to get an astonishing amount of wear out of each item. I was just looking through what I've bought from Outfittery since I started getting those boxes. It's 9 items over, I think, 4 boxes, and every single one of those pieces is a staple in my wardrobe. Similarly, there are a number of items I got from my old box - so a while ago now - that are still going strong years later.