You could simply use Titan one or Titan 2 and use mouse\keyboard, however it needs to be connected to a PC (Titan 2 probably works with keyboard and mouse without PC, I have no idea, but ask in the forum first if it works for switch before buying it).
I have CronusMax which is very similar to Titan one, but CM has no Switch support, however on supported consoles I can play with mouse and keyboard like on my PS4...
You can't just connect a mouse to the joystick output because it requires a lot of processing of the joystick to the mouse and it doesnt work good on all games, the game on max sensitivity settings must also have a lot of speed natively or else it will never work good, because the mouse is emulating the joystick, it works good on PS4 on games like Battlefield and COD, but some others it doesnt, on CM we have user settings in the forum to get an idea, but they depend a lot on the mouse too.
EDIT:
This is an example:
However he is using 2 adapters as he is using CronusMax which doesn't support Switch, but with titan one or 2 it probably doesnt require anything else other than the PC and Titan 2 might actually not even need a PC as it has a lot more processing power and memory maybe they made it work without the PC (again you have to ask in their forums because I'm not sure).