Keeping whites actually white

A few years back I started amassing white towels for my bath and kitchen. The thought was that they never go out of style, they would simplify my putting them away since it’s not decor specific, and that they might be easier to clean since they would all just go in the same load of wash.

Fast forward a few years and I am finding myself wanting to replace many of them because they just look dingy. I was hoping to have them last several years and replace based on wear, not looks.

Does anyone have any hacks for getting dingy whites clean again? And keeping them that way?

I am pretty much a cold wash only gal and have not tried bleach or any other brighteners yet. I try to stay on the no chemical/natural side of the fence where it makes sense.