Recommendations for smart temperature sensors

It's hot here in Germany at the moment, and I've found a new hobby: experimenting with different ways to keep the flat cool. Unfortunately, right now I'm doing that mostly on gut feeling, and I'd like to add some data to the mix so I can pretend that this is Serious Research™.

Does anyone know of some good smart thermometers that I can use both inside and out, and that I can regularly take automatic readings off? My main criteria are roughly:

• Reasonably waterproof and battery-powered - I'd like to put at least one on my balcony which isn't covered, so I want to be confident that it survives out there.
• Relatively cheap - I want around 4-6 different thermometers spread around the inside and outside of the flat to see how the sun's position affects the temperature, and I don't want to spend more than around 100€ on this project in total.
• Scriptable - for the data collection, my plan is to be able to run a script on a spare Raspberry Pi to download all of the data and potentially send alerts when something changes or when it makes sense to start opening doors and windows to cool the flat down.
• Not too complicated - looking around, some thermometers seem to require smart hubs and online accounts and things. Ideally, I can avoid all that - I want something that I can connect to from my home network and download data from as I need.

Right now, I've found a few different smart temperature sensors that I can buy off-the-shelf, but these seem to be on the more complicated end of the spectrum, and require central hubs and uploading all the data to clouds and things like that. Ideally I can avoid that. Alternatively, I have some RPi Pico boards at home, so if I can buy some sensors that I can connect to those, I could get those set up more simply. But with the DIY route, I'm worried about weatherproofing, especially if the temperature sensor needs to remain fairly exposed for an accurate reading.

So: do you have any recommendations either for simple smart sensors that I can buy, or for sensors that I could easily stick to a Pico and leave outside for at least the rest of the summer months?