I use softs all the time for interview and product shots. The only problem I have in very small rooms is spill from a too wide source which can be overcome with egg crate grids or flags and cutters - or even a flag made of "blackwrap"- a black annodized aluminum foil.
Three point lighting isn't etched in stone. Often I use just the softbox as the only "source", placing it 30deg. off center so I get a darker side of the interview. Occasionally, if the shot needs separation I'll hit it with a 150-300w. fresnel if I don't have a natural source in the room like a table lamp or window.
Alternatively, pointing that 300w. fresnel to the wall with a wash/slash/poof/glow/(insert your favorite look here) works if you don't want a backlight or don't have the room for separation. You can also use color gel on the light to accent the room or the person.