Why do we call luxurious living a "posh" existence?

In the days of their empire, British tourists travelled by ship from England to the warmer climates of India and the Mediterranean. Wealthy passengers on these voyages demanded cabins shaded from the sun, which meant being on the port side on the way out and the star-board side on the way home. Tickets for these cabins were marked "POSH," which stood for Portside Out, Starboard Home, and posh