Good one!
I'd say none of the previous members of the Confederate government during the Civil War, most of them were getting older and were very tired by that time. And I'm not sure how many would get along with Forrest or vice-versa!
Surfing quickly, I'd say for a start:
Vice President: Joseph Emerson Brown of Georgia, strong believer in Southern rights.
Secretary of State: Isham Green Harris, former governor of Tennessee, outspoken ally for Forrest.
Secretary of the Treasury: John Henninger Reagan also continues in his post, he was a very able administrator in his Postmaster General duties, he does as well as Treasurer.
Secretary of War: John Bell Hood, aggressive if impetuous former CSA General.
Secretary of the Navy: John L. Porter continues Mallory's work on ironclad steam warships, improving the CSN to a world class navy.
Attorney General: Wade Rutledge Keyes continues his strong stances under Forrest.
Postmaster General: Drawing a blank here.............
Surgeon General (Or equivalent post): John Allan Wyeth, who also forms the Confederate States Medical Association.