Hi Phil, and welcome to the WeatherCat forum!
I took a quick look at the WeatherHawk 916 brochure and quick start PDF files. I didn't realize that WeatherHawk does not use a Console for visual weather information, relying solely on being connected to a computer. Most console based systems have their barometer and indoor temperature and humidity sensors in the console.
I can't recall anyone here having a standalone temperature sensor. The developer, Stu, can suggest any products that he has tested with WeatherCat. Even getting a very basic USB weather station and just using it for indoor temp/hum wouldn't work, because WeatherCat (or any other software that I know of) can't bring in data from multiple weather stations.
I'm sure other members will join in welcoming you, and may have an idea to help. Stu will have the definitive answer, though.
Glad you found us,
Steve