I tested a very easy to use 404 plugin by phpbits.net
A video walk through
Taking a closer look.
After installing the plugin the settings are inside the Appearance -> 404 page
The Pro version includes a few more options:
Such as adding a logo, a menu, 3 layout options, typography, scripts and logs.
With the pro plugin I added a logo, a menu, hide the 404 number, left the title and content as they were, and made some additional adjustments to the search bar and Go to Home page text link.
The 404 plugin by phpbits.net is very easy to use and has a comfortable to use UI. Check it out at https://wordpress.org/plugins/forty-four/.