These days it is very easy to self learn in any subject.
Pi's open up a whole world of stuff, not just coding, which I'm still learning too.
Visit the sensor sections of Adafruit, Sparkfun, Seeed Studio, Digikey, Element14, RS components etc.
So many types these days. There are even tutorials.
Back in the old days when I started I had to use velostat foam and two bits of foil.
Velostat was the antistatic black foam semiconductor chips had the legs stuck into so ESD did not kill them.
Plastics with high carbon contents can be a bit conductive, even those antistatic pink and blue bags can be a little conductive.
I did a google and there is now conductive silicone and even bio versions.
Not sure if there are 3D printers for silicone, if not someone should invent one
TPU is polyurethane rubber that is printable, is there a conductive version?
Dual print head 3D printer could make some interesting sensors.
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges