Yes, you need a new trim piece. The official matching honeycomb patter one is about $130 for an official part, but can get Chinese ones from AliExpress for about $40.
Yes, 7C0919606 is the most ideal swap (in terms of buttons), also the most rare and expensive. Only difference between that and the 6.5", is that the top left button says "Radio" instead of "Band". Same function.
5NA919606 is another non-nav option. Couple buttons different; top left is Radio vs. Band, bottom left is Mute vs. Voice, and top right is Setup vs. Mute. No idea how those buttons function.
5G0919606 is a Nav option that can be used. The Mute & Sound buttons on the top right are replaced with Nav and Traffic. The buttons won't do anything, you'll loose the Mute button, and Sound settings can still be accessed through the setup menu. That's also the cheapest and most available 8" matte option.
All of them are just plug and play. It's about a 10 minute swap. Pop off the trim, pop out the screen, unplug 2 cables. Do that in reverse to put the new one in.