Assuming you don't have a metal roof, foil-backed insulation, lots of metal studs and/or metal HVAC ducts close to the antenna, then almost ANY antenna you put in the attic is going to work better than something on a lower floor (and of course not as well as a rooftop mount outdoors). You may want to test what sort of signals you're getting in the attic by putting up the simple wire-version of this antenna in the attic -
Homebrewed Off-Center Fed Dipole - The RadioReference Wiki
Scroll down the page in the article to see the wire version. You can make it in about 15 mins and for $10 or less. Mine worked so well in the attic that I built the copper pipe version.... and left it in the attic. I have unused CATV cables in the attic so I simply connected the OCFD antenna to a splitter and routed it to the old CATV system in the house. Now I have a scanner antenna "outlet" in several rooms of the house on both floors (where the old CATV outlets are). BUT.... you certainly can put just about any antenna in your attic if it fits... and usually get better results than from a lower floor.