I was tempted at first to get a commercially available weasther station that publishes its data, such as netatmo. But where's the fun in that? So I looked into sensors. I already have a bunch of DHT22s and DS18B20s. The DHT22 would get me temperature and humidity. The DS18B20 only temperature. But I also wanted at least atmospheric pressure. So I went for the Sense Hat (aka Astro pi) which provides a number of sensors including temperature, humidity, and atmospheric pressure.
I originally wanted to have both the Sense Hat and a DHT22 as reference, but it's not easily done since the Sense Hat hijacks all the GIPO pins. For now I'll rey only on the Sense Hat and see how reliable it is.
Next step: hardware