I would definitely go with a base station antenna, and not a mobile antenna. You can fit a discone in just about any attic, and they are available everywhere. Some Radio Shacks even carry them in-stock, although that is becoming less common as they seem to have forgotten that RADIO is their first name. They need to change their name to "iPod and Cellphone Shack", but I digress.
Anyhow, in Katy, you should do very, very well with an attic mount antenna. You might start to get a little static from weak stations west of downtown. Especially the 800mhz systems. And especially on days when your wood shingle roof is waterlogged (which is about 359 days a year in Houston, isn't it, lol? Those wet shingles -- with the aid of any tall, thick trees around you -- will suck up those high frequencies pretty quickly. But you'll do fine on UHF and below.