I want to setup my SSH connection correctly. As many tutorials told me, it is not recommended to use the root account of Ubuntu server. So I would rather use my standard account "Simon" to upload files and transfer terminal commands.
When I run 'sudo su' I am prompted to type the standard password for my user account Simon in order to gain root permissions. I am pretty sure, that instead I should get asked for the root password, shouln't I? How can I fix this?
No, you should not.
If you were to type "su", then that would be true, you should be asked for the root password. Su basically means "switch user".
Sudo authenticates the logged in user again to make sure you did not leave the terminal open in order to allow you to use the permissions given to you via the sudo configuration (/etc/sudoers, /etc/sudoers.d/*).
As such, you cannot fix it because that is the desired behavior. If you still want the behavior you are describing to want/need, sudo has a configuration option called runaspw.
Also, try not using sudo su but rather, "sudo whatever command I'd like to run as root".
