You have a good recommendation, but if you have not yet visited the Civil War Museum in Ft. Worth, then it should be at the top of your list.
Just by accident, I got a motel room that was perhaps 100 yards from the Museum of Southern History in Sugarland, Texas (suburb of Houston). It was by far the best small museum I ever visited. The former building is a replica of Thomas Jefferson's Poplar Forest house with amazing detail, even applewood floors. And the entire second floor was dedicated to Civil War history, including a stunning 24' X 8' mural of the 2nd Battle of Galveston. The museum has moved elsewhere to a college campus in Houston.