I'm a bit surprised that you don't seem to have an equivalent of the Handysignatur [0] (eID based on mobile phone) we have in Austria. It's getting more and more popular here, I guess because all you need is a mobile phone (who has a card reader after all?).
I find it incredibly convenient as it gives you immediate access to a growing list of e-government services [1], as well as signing PDFs and even things like a service for cancelling subscriptions online [2].
[0]: https://www.handy-signatur.at/hs2/home.aspx?language=en
[1]: https://www.handy-signatur.at/hs2/?site=infos/applications