For general size comparison, I find that the younger the market it caters for, the smaller the sizes. M&s, next Matalan all run up large, Dorothy Perkins in the middle, Topshop, boohoo etc all smaller. H&m make it up as they go along.
Your sizing suggests that you are quite slim hipped which works well with Zara. As a very broad rule, XS=6, S=8, M=10, L=12, XL=14. You will probably get away with a 10 in bottoms, S in loose cut tops (lots more are meant to be oversized than you realise), M in fitted. I would go for M in jacket because the sleeves aren't always the most generous. Anything in the TRF section runs up smaller, sometimes massively so, as that's the range aimed at a younger market, basic sizes up Large, woman is generally true to size. Shoe sizes are narrow.
And the Birmingham bull ring store is meant to be good 😊 if there are things that you like on the site, take down there numbers as stuff gets rotated a lot quicker in the stores so there's a good chance it will be in the stockroom. New styles arrive twice a week, so it's forever changing, although they will be winding down on summer stock now ready for winter to start being delivered in June. Mad, I know.