Best material for instrument for SEN school

Hello,

I am trying to build a musical instrument/sound installation for a SEN school. Something similar to this.
I am using a 'MPR-121 board' from Adafruit.
The instrument should be 'robust', so that the children can 'jump' from one sound to another and ist should be easly disinfected (due to the actual pandemic). So I am looking for the best material as contact parts. The material shouldn't be noxious in any way, since the children will probably have skin contact. Also, the material should be affordable, but the financial part is the least important.

Do you have any suggestion?

Furthermore, I am wondering if it might be able, to get the MPR121 also to recognize 'touch' when the children are wearing shoes. But with the code provided by adafruit I can only get direct skin contct to work.

Thanks for your help

Andreas