Check out the DIY section for some ideas, and I’ll pitch my sensor design as an option (it also has temperature/humidity plus an OLED sreen for local display). I’m working on some improvements now to make it modular and accept more sensors (luminosity, motion, environmental, etc…)
I like distributed sensors, running on ESP8266 boards (cheap, WIFI enabled with a good # of GPIO pins for multiple sensors). Using ready-made firmware like ESP Easy or Tasmota also makes these devices super simple to set up. The protocol of choice for getting the data into openHAB is MQTT.
Arduinos are cool for prototyping and such, but to get a finished, wifi-enabled product, you need to put in more $ (an Arduino Uno + Ethernet Shield will cost a lot more than an ESP8266-based NodeMCU board).