I am reading Microsoft documentation on how to sign a driver for windows 10 X64 and I am getting different information from the Microsoft website.
This document explains how to sign a driver by the developer without the need to send it to Microsoft.
This document explains how to submit the driver to Microsoft for signing.
and on other sites, the information is very different.
I need to sign my driver which I will send alongside my hardware to the user (so no need to be part of the windows update).
How can I sign it? which procedures should I follow and which certificate should I buy?
Since you are developing actual kernel-mode code, you need an EV certificate, which you will use to submit drivers to the "Windows Hardware Developer Center Dashboard portal". See the announcement here:
Driver signing changes in Windows 10
Just in case this requirement changes in the future, I recommend signing up for the portal first and looking through its user interface and/or documentation to figure out what the current requirements are before your invest in a certificate.
After you submit your driver to Microsoft, they will apply a signature to it that will allow it to be distributed to the end users; you shouldn't have to worry about the details of that signature.