You're rarely going to find good basics in cheap shops because they have to differentiate on 'design'. The same goes for t-shirts, if you want a plain t-shirt you first have to avoid anywhere with surplus graphics, pockets, buttons, whatever.

If you look further you can find high-quality denim and t-shirts in a variety of cuts. Even bespoke. But they differentiate on quality and things that matter to enthusiasts, so a brain poisoned by mass-produced fast-fashion will wince.