It makes no sense at all to be wearing ‘nice’ clothes when you’re handling paint, surely?
Aside from Amazon and eBay, etc, Google threw up these workwear options:
https://www.aardvarkclothing.com/
https://www.workwear.co.uk/
Depends how much you want to spend and how much time you have for browsing. But you should definitely have a separate wardrobe for paint clothing.
For non-work day to day - 14 years is a long time in black leggings …
Treat yourself to some wonderful, colourful t shirts, sweatshirts, and hoodies, plus trousers, dresses, knitwear from:
https://communityclothing.co.uk/
They’re not the cheapest option, but ethically sound and brilliant quality, so the clothes will probably last years and years.
If much too expensive:
https://www.uniqlo.com/uk/en/home
also has all you need for everyday life, at lower prices but less satisfying provenance and fabrics.
If you want to dress up - look to Zara, but only things in a silk, cotton or linen mix at the higher end of their price range. Inspirational styling but variable quality.
Or have a look at places like:
Plumo
Farm Rio
Free People
Gather and See
YMC
depending on your style preferences, and see what’s available by them pre-owned. (Far more satisfying than endlessly trawling Next.)