I'm posting this for the benefit of korttoma, because he's a Hero member who asked for it. It's an interstitial board for a 3.3V 8Mhz Arduino Pro Mini and an RFM69HW and an Si7021 TH or BME280 THP breakout board. Here's a photo of what it looks like: https://forum.mysensors.org/uploads/files/1476660793260-promini.jpg I recommend you remove the LED that's on Pin 13 of your Pro Mini, which you can do either by desoldering it or even just thoroughly scraping it off with a knife.
The current version is version 015.
Aliexpress or Ebay link
4pin I2C Si7021 or BME280 TH sensor breakout board
female header pins
2.54mm pitch (same as 0.1" pitch)
male header pins
zipped files attached
1 piece of wire of the appropriate length for the antenna