Make the 'dough' yourself!
Squishy Circuits is a company that makes two types of dough (one that conducts electricity and one that insulates) for making fun, colourful electronic circuits. Fortunately for us (and I'm not sure why it works for them... but anyhoo) they have given away their secret formulas.
Actually, the first one's not so secret, it's just plain old playdoh. The second, however, has no salt and is carefully formulated not to be conductive.
So here are the formulas:
And are two videos - one about insulating dough and one about conductive dough:
Note - alum (or aluminium sulphate) is mentioned as an ingredient in the insulating dough. This can be purchased cheaply on Ebay in small amounts.
Here are some ideas for squishy circuits:
Here is a good lesson plan for Squishy Circuits: https://www.energy.sc.gov/files/Squishy%20Circuits.pdf
And here is a good instructable: https://www.instructables.com/Squishy-Circuits-in-the-Classroom/
Big educators guide: https://www.teachersource.com/downloads/lesson_pdf/Squishy-Circuits-Curricula.pdf