To have 1:1 mouse movement go here
AppData\Local\TslGame\Saved\Config\WindowsNoEditor
and open gamerusersettings.ini. There's a new command called MouseVerticalSensitivityMultiplier. Change it to 1.428571. Save and put gamerusersettings as read only. That's it.
Changing your sensitivity via ini is safe. If someone has doubts, set the value with the in-game slider to 1.42. It's not the same as it lacks 4 decimals but it's at least something.
To remove the previous fix, just delete input.ini (or remove everything from it, it should be blank) from the same folder, remove read only from gamerusersettings.ini and launch the game once before applying the new fix. If gameusersettings is still set to read only you will not find the new sensitivity command.