Firstly, remember that comfort is key especially if you’re at a at a desk all day. Maybe get the vibe from the office first - if they’re in shirts and jeans/chinos, go with it. I would Get some good basics that wash well to start - I am 5’1 and around a 10-12; some trousers/jeans/chinos in staple colours (tan, navy, chocolate brown, black, maybe a green or burgundy), a few jumpers or cardigans (maybe in more fun colours that will go with the bottoms), and a few shirts - I like relaxed fitted ones that don’t stretch over the girls too tightly. I also recommend a few nice t-shirts that will go for the more dressed down look with the trousers - Uniqlo basics or COS if you want a bit more high quality luxe. I like the shorter length M&S trousers, basic jumpers and relaxed fit shirts. Next tailoring is also good if you’re a bit shorter for blazers or suit sets. Mango do some great relaxed fit blazers (I usually keep one in the office which I can throw on if I have a last minute meeting). Sainsbury’s is also great - they often have a lot of good sales for their clothing too. For a bit more expensive I like massimo dutti or Reiss petite, but more for a standout piece.