The old 300 ohm trick was 30.5 inches of 300 ohm (flat double strand TV wire) with the ends twisted together and the middle tapped to yield two separate lines to feed the FM receiver. Today with a 75 ohm feed on all the receivers I would say the same length as a car antenna would do it, unshielded. Use shielded coax to that point. I do what you do, though. Hang a piece of damned bell wire out of the back plugged into the little hole on the 75 ohm connection, tape it against the wall when I find a good spot and let it go at that. You can spend US$50 to US$100 for a real jazzy indoor antenna and like amounts for outdoor ones.
I used a deep fringe FM antenna years ago in central Connecticut to pick up Springfield, Hartford and Amherst. When the Amherst station, WFCR, went off the air I sucked in station north of Boston, sweet and clear. Yup, good outdoor antennas are a must for good sound. Likewise, in Plalo Alto I used a good FM antenna for San Francisco, about 35 or 40 miles, straight line, and got sound like I was on a wire to the studios. As usual, YMMV.