What part do you want to be simple? There are usually compromises to be made e.g.,
- use wireless very simple from an installation point of view, can be battery powered so no restrictions on placement of sensors
- create a single wire protocol is very simple aka cheap but more difficult from a protocol point of view
- use multiple wires is very simple from a protocol point of view because you can separate IN vs OUT and clock signal. This eliminates timing issues. But this requires more wires.
- another important point is what peripherals do you have available just UARTs and I/O or maybe a CAN bus peripheral