Try the LTC3786:
http://cds.linear.com/docs/Datasheet/3786f.pdf
They use an N channel FET and high side drive it. They use the body diode as the standard rectifier diode, then short this out with the main FET channel once this diode has started to conduct to obtain better effiency. However, with this architecture (and the one described above with the Schottky diode) you cannot disconnect the input from the output. If this is a desirable feature, use a buck-boost controller (LTC3780/3789)