Luckily, Switzerland has a nice bike trail network which can be easily accessed for planning purposes via a web interface: https://www.schweizmobil.ch/en/veloland/veloland.html
We were taking trail number: 5, 41 and 53. Although some of these trails need to be shared with cars, normally you can count on having either quite silent roads or specific bike tracks that you only share potentially with hikers. So the infrastructure is quite nice compared with other countries and until today, we only had good experiences made on these cycling tracks. Of course, no GPS is needed – these trails are well marked.