Suggestions on conductive materials for textile capacitive pressure sensors
There are several options but the one that comes first to my mind are piezoresistive materials, especially polyester yarn incorporated with carbon.
This material is well documented and a lot of research is done around this material, so this might be a good starting point.

EDIT : Yarn used as the dielectric material between the two plates of the capacitor is more appropriate here.

Readings: 


Study of Structure and Properties of Polyester/Carbon Blends for Technical Applications
Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint 
Textile capacitors as pressure sensors
Design, Development and Characterisation of Piezoresistive and 
Capacitive Polymeric Pressure Sensors for use in Compression Hosiery