Another input method is shown in the following video [1] where each symbol get its own command, e.g. \mbfitx is equal to {\bi x}. The source table mentioned in the video can be found on the STIX page [2].15. September 2016 um 19:44
I use Xcode on MacOS (former OS X), which has very good Unicode support (including RTL scripts). There is a Unicode symbols table, but it is slow. One can also design one's own keyboard map, but that is very time consuming.