I’m 34 and in the past few years have moved to better quality clothes, my favourite stores are:
Sézane - great for knitwear, blouses, dresses
Rouje - for dressier options and summery styles
Bellerose - a new find, only got a jacket from there so far
The Kooples - only got a couple of bits
Realisation Par - dresses for parties, weddings etc
J Brand, Frame, Citizens of Humanity for jeans (often via The Outnet)
Vestaire Collective, Depop, Ebay for second hand designer items
&Daughter, Knotty Ones, Oubas, Genevieve Sweeney - knitwear
Maje, Sandro, Kitri, Stand, Shrimps are also places I browse but haven’t got much from.
I like Liberty, Selfridges, Net-a-Porter, Outnet to browse and they often have lots of different brands - a good way to explore what brands might fit your style.
You don’t mention budget, I don’t mind spending on quality but I also keep an eye out for sales - recently got a couple of pairs of jeans from Liberty for £70 ish each - reduced from £250 or so. A lot of the others places I’ve mentioned have good sales twice a year.