Do a clean install. If not already done, make a separate /home partition so you can change os fast and effortless.

I would love an foldable case with a keyboard on one side. Like a little Laptop. Would be so neat.

Edit, something like this:

You can untick the other providers. I found this one for example.

25€ for 15G is also way too much. I now pay 5,99 for 7GB. (Also germany, monthly cancellable, sim.de [No advertisement])

You should look here for good prices.