As someone who has studied swordplay to a certian extent,
my ideal blade length in actual combat is between 12-24 inches. While I'd rather be using a european sword (like stated in my post above about the schiovana), I realize that for pure function, Japan is where you should look. That being said, my suggestion would be to get the parter or companion to the katana, the
wakizashi. Indoors, the wakizashi is obviously more effective than a katana. It is light, one or two handed, strong, and can be primary or off hand in combat. I imagine that wielding two could be effective under many scenereos. They are also more easily concealed.
Unfortunately, I do have to agree with Long. I have swords in my house, and if someone broke in, I might use them, but I'm just as likely to use a kitchen knife, chair, clock, wife, coat hanger, or drapes in combat. There are situations where swords are appriopriate. There are situations where swords are not appropriate.