My carhartts are double thickness on the knees I think they can take knee pads too. Filson double tin cloth bib trousers are my favourites, no knee pad pocket, but the double layer of waxed cotton is pretty good at protecting my delicate knees (had 3 knee surgeries so far).
Anyone wear work dungarees? Worn Carhartt cotton ones for years but need something that can take a kneepad easily.