Bloody hell OP, you look incredible, well done!
Anyway, Vinted. After a lot of trial and error on there, I only use it to buy good quality items in brands I'm confident I know the sizing. The postage prices have gone up, so it's just not worth buying anything cheap on there.
I've had luck with some designer vintage finds (e.g. a rare Vivienne Westwood gold label jacket), and for high street I look for Cos, Arket and Massimo Dutti.
Your best bet would be to spend some time in real life working out what you like in terms of brands, cuts, fabrics, colours, silhouette etc. Go round the shops and try things on - take a tape measure and note the actual waist, bust, lengths.
Then you can ask the Vinted sellers for measurements. Always get pics of the labels on the item too, so many sellers list in the wrong size category.
It's a lot of legwork, but worth it to start building a wardrobe you actually love. I'm in the process too and enjoying it.