first off, discs dont warp!,the webbing between them prevents this,technically what happens is the discs get hot ,and when you stop and sit with the brake on ,you squash a section of metal on the disc,this contracts ,and gives a pumping sensation to the pedal,caused by high spots on the disc,,so most discs that run cooling holes are better at preventing this,while grooved give a clean pad for better grip on the disc.

i think your wheels need balancing
or maybe a tyre change! deflex do the steering bushes,there a bastard to fit,i done mine,not much room to wield your spanners,pluss you get covered in shite,tip,go in at the wheel arches after removing the liners.

check your bearings too.