Clothes for a Saturday job

[TheDeathAndGlories]

I'm skint but I need some basic clothes for Saturday job interviews and for the job. I only really need one outfit but things have changed a lot since I last needed such things.
What do I wear? Before I would have bought a pair of cheap black trousers from Dorothy Perkins but they don't exist anymore. Also shoes. They need to be flat but I can't wear ballerina etc as I look top heavy.
Help

Primark or Next? Plain black or dark grey trousers and a white shirt-or black fitted top maybe?
I don't think being top heavy stops you wearing ballet type shoes?

Not many options unless you go for a Mary Jane style or T bar.

Sorry I meant to say from the tall section
And that I need to need to buy online. No primarks here I live in fat face country

I had forgotten about next, do you need an account?
Will look for some leather/fake leather Mary Janes