Continental makes some urban tires with several protective layers, like the City Ride. Heavy though, and not particularly fast, but great flat protection:



I think you really owe it to yourself though to figure out what caused the other tires to go flat. It could have been something as simple as pinched inner tubes. Or it might be glass, tacks, goat heads, or who knows what?

I like to sit under a nice bright light and feel the inside of the tire where it contacts the tube, checking for anything poking through. Then use a knife blade and tweezers to completely remove it like you would a sliver in your finger. Once you figure out exactly what caused the flats, you'll have a much better chance of avoiding future ones, otherwise you're just throwing money around trying different tires and tubes.