If you already have a RPi, you can get the SDR from NooElec.

https://www.amazon.com/gp/product/B00VZ1AWQA/

It has a small cable and antenna, works well if you have a window which is not blocked from buildings. I am currently uploading data to Flightaware, FlightRadar24 and Plane finder. Installation was pretty simple.

I’m running HA to show all the different sensors (PV/Energy/Battery a.s.o)

HA = Home Assistant?

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USB-C is somewhat a must. The Shelly temp sensors with batteries seem to be horrible and I don’t want to swap batteries once every few months…

The Shelly temp sensors are battery hungry because they're WiFi based. Zwave, Zigbee, or even BLE or 433MHz based sensors will last at least a year on a single set of batteries. I purchased some cheap Xiaomi LYWSD03MMC units over two years ago, and the CR2032 batteries are just now starting to need replacement.

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Any recommendations? I don’t have any smart home hub yet so I assume I need f.e. A zigbee hub in case I go for zigbee sensors?

Depends on which protocol you end up using. Aside from Zigbee, I've also used RF433 and BLE based sensors:

If you're already using Home Assistant, you can install ESPHome on any ESP32-based device and use it as a Bluetooth Proxy hub. I already had some ESP32 smartplugs and bulbs flashed with ESPHome, so it was as simple as adding a couple more lines of code to get a few BLE Proxy hubs, without needing to purchase any additional hardware for the hub(s).

Switchbot, Govee, ThermoPro, Inkbird, and Xiaomi all make fairly popular BLE-based temperature sensors.

Another option is an RTL-SDR antenna like this, paired with the RTL_433 add-on in HA. Then you can use any supported 433MHz sensors like this and this. 433MHz isn't a mesh network like Zigbee, but it does have longer range, doesn't require any pairing, and the sensors send updates every 16s, and take standard AA or AAA batteries.