I found some leaf springs for not too much, and they're made specifically for Mavericks (says custom fit for 74', but they're all the same.)
Yeah, from what I've read you can't go wrong with the JC Whitney springs if you're looking for stock replacement with a little more load capacity. Lots of people on here use them.
Once upon a time in the 70s I added leafs from a station wagon to mine. Kept the large top leafs bolted in, removed the lower leafs, and added the lower leafs from the wagon. A few C-clamps and a longer center bolt was all it took. Jacked up the rear pretty high without needing air shocks. Rode like a station wagon, too.