For good quality affordable basics I personally recommend
Cloth & co
AS Colour
assembly label
Saba

• atmos & here, has some good plain basic T-shirts and jersey lounge pants but don’t get anything fancier than that

• huffer, pretty solid choice for plain shirts and sweaters

• primness, their simple dresses are good quality, wait for a sale for them to be affordable

Sports brands are generally reasonable quality when it comes to basic Ts and sweats, just wait for a sale if not affordable at full price

For good somewhat expensive basics to invest in probably Gina RTW