The small antennas like the flatwave you are currently using are really only good for locations near the broadcast towers, where signals are strong. You don't want anything advertised as an 'omni-antenna'. They generally are not any better.
Normally I would have suggested something like the ClearStream C2V with the reflector removed, but now they've come out with the
ClearStream 2Max. It does not have a reflector (which makes it bidirectional) and, if you aim the flat side north/south you should get most of the channels in green and yellow (though maybe not all of the LP channels). Make sure to get the best clear line of sight both north and south. And use a good quality coax (i.e., RG-6 and not RG-58)
If you purchase it somewhere with a good return policy you can get a refund if you are not satisfied.
Given your almost-acceptable experience with the flatware I think you'll be happy.
You can also consider trying it in your attic, though attics are not friendly locations for antennas. But whether you mount it on the roof or in the attic, test it before permanently mounting it or drilling any holes for cables. Sometimes a few inches one way or the other makes all the difference.
If you mount outside, make sure to ground everything properly.