I no longer work manually but in the latter years of my manual existance I could only ever wear 'cargo pants'. They are mostly designed with an elasticated section in the waist but it's the thigh pockets I found I couldn't live without. They seem to wander in & out of the fashion world with alarming regularity but a well stitched, medium weight material, 100% cotton pair can still be had for £15ish.
From personal experience, stay well away from any outlet specifically aimed at 'the trade' & stay well away from any of the 'brands' that they carry . . . ie. Dickies.