the sweboz were one of my earliest campaigns, and i found a method that i felt really worked. it's simple, but effective:

spearmen + archers, ratio of about 2:1. the spearmen can really hold their own in most fights, especially if they are paired units. and i mean the toughie spearmen - not the levies. Dugunthiz i believe they are called. and the archers, Skutjanz, just seem to cut through most opposition in the early game.

If you need an added punch, the FMs' bodyguards can really hand it out. So spearmen+archers+FM equals killing maching. Not the most adventurous selection, but it worked very well for me.