The main problem with softboxes is their size - get them far away enough to light a figure and they become more like a point-light source.
I often "build" a softbox with a strip of translucent fabric draped over a boom, and sometimes will mask the sides with black duvatyne or felt. Sometimes I end up with a Box made from three or four c-stands. For low-key stuff, I really like a 6' high strip light, maybe a foot or two wide. Panel systems can be really helpful for these kinds of setups.
If your room is small and you're using umbrellas, get a few yards of wide black felt (it's lightweight and cheap). It goes a long way in helping you control all the dang light bouncing around the room when you need a little more contrast or drama. Cover a problem wall with it using blue painter's tape - super handy, and you can cut down problem windows with it, too.
In this shot, you can see the "strip light" reflected in her shades. A Speedo head behind a strip of diffusion, maybe 6' high by 12" with 2' of black duvatyne on each side, sewn by a sewing-grandma-lady (find 'em at the fabric store, ladies who make draperies and curtains can make photo scrims in their sleep) , and a grid head on the background.