They used to list Yaz as 6' at some points in his career. They also used to list his weight as 185. Both were exaggerations. He wasn't quite 6', but he was probably 5'11". I met him in person right after he retired. He was wearing cowboy boots that made him look a little taller, but I still think he was about 5' 11. His playing weight was usually around 175, based on interviews that I have heard and read.
Nava is about the same size as Pedroia, who is listed as 5'9", but that is also an exaggeration. Steve Garvey was a small first baseman, but like Yaz, Garvey was big on talent. Nava is not very talented at all.