The DB411 is a good choice. Telewave makes some similar folded dipole types. I will make a specific recommendation that you not consider Telewave fiberglass collinear antennas, however.
Depending on the site conditions, 9db might be excessive. Unless you get an expensive antenna with null fill, they have a lot of holes in the vertical pattern above and below the main lobe.
Keepest thou thy airspeed, lest the ground rise up and smite thee.