Howdy from Oklahoma.
If it's just a driver, another 12-bolt should be plenty adequate. I presume you have a 454 from your login name, if your right foot is heavy or you're towing/hauling a lot you may want to go to the 14 bolt (either full float or semi-float).
Just FYI, if you're can do the modifications: the 1988-up Chevy truck 5 and 6 lug 14-bolt semi-float axle, which with modifications, will work under the 1973- 1987 trucks. The 454 SS trucks used the 5 lug version so it's kinda rare. The light duty 2500 and some 1500 4x4's used the 6-lug version. It would be a heavier duty axle than either a 10 or 12-bolt but not as heavy as a full float 14-bolt.