My first guess: - find the sensors you want on Digikey or similar https://www.digikey.com/ https://www.digikey.com/ - design a PCB for those; everyone has pr

My first guess: - find the sensors you want on Digikey or similar https://www.digikey.com/ https://www.digikey.com/ - design a PCB for those; everyone has preferences, but here’s some common choices https://www.raypcb.com/online-pcb-design/ https://www.raypcb.com/online-pcb-design/ - get that PCB manufactured, eg at OSH Park https://oshpark.com/ https://oshpark.com/ - solder your parts onto that board - model a housing; get 3D printed Congrats — you have a prototype! You can do all of these steps through free tools or moderate fees; people can and do design their own electronics this way.