You'll see larger buttons on officers' frocks, and conversely you'll sometimes see 3/4" buttons on greatcoats. I seem to recall a private-purchase enlisted frock having larger buttons, too, though I could be wrong. Generally, though, you'll probably want to replace the buttons on the frock.
Marc A. Hermann.
The Daybreak B'hoys.
Liberty Rifles - Hardtack Society.
Oliver Tilden Camp No. 26, SUVCW - Co. I, 83rd NYV, SVR.
Descendant of Pvt. E. Hermann, 45th PA Militia - Capt. Wm. K. and Lt. Geo. W. Hopkins, 7th PA Reserves - Pvt. Jos. A. Weckerly, 72nd PA Infantry - Pvt. Thos. Will, 21st PA Cavalry.