Vinted, but be clever about it.
If you know your size in standard brands like M and S, you are unlikely to go terribly wrong. Ask for measurements, only buy things with comparable measurements to things you already own.
Buy only new or worn once shoes that have pictures of the soles, just someone forgot to take them back to the shop. No other shoes.
Buy things on there through the 'material' filter, I set mine to cotton, linen, leather, wool, merino, those things look far more expensive than they are, and fit with the vibe you want.
Buy winter coats on there, so many under-used or hardly worn older wool coats, some absolute bargains, I would be buying more if I wasn't on a coat buying ban. There's no way you can get that quality and linings in the shops currently on a cheap budget.
Create your list of brands you'd like to own, search those.
If you do make a mistake, resell it immediately with more information on there about size/why it didn't fit. I bought a stunning tweed coat recently but it was just too big for me, I resold it immediately for the same price including my postage and the person who got it loved it.
Mix in with some charity shop and the odd new purchase to vary your life and stop Vinted obsession.