If you only need a Temp & Humidity sensor (not a full Weather Station with display, etc), you can try:
- Sonoff TH10/TH16 - https://www.itead.cc/smart-home/sonoff-th.html
- Sonoff Sensor Si7021 - https://www.itead.cc/wiki/Sonoff_Sensor_Si7021
- Sonoff-Tasmota (Software) - ITEAD Sonoff switches and sockets - cheap ESP8266 Wifi+MQTT hardware