need pressure sensitive material

i want to make a sensor that i lay on top of on a mattress which can
indicate where the pressure points are. specifically i want to have
two thresholds, one indicates that pressure is in a middle range, and
another when pressure is even higher.

i am thinking some kind of pressure sensitive foam or rubber that
changes resistance when pressure is applied would work. this sensor
needs to indicate that pressure anywhere on its surface has exceeded a
certain threshold. it does NOT need to indicate where that pressure
point is on its surface.

are there any pressure sensitive foams out there?