There are no arrivals lounges at any Australian airport. BA uses the QF lounges, and if you have access to any departure lounge, you can use the showers there. The BA horizontal bed has several disadvantages to the QF flat but not horizontal bed; it is smaller, narrower, harder to get into/out of, has less storage space and doesn't have a massage function. Many people prefer the QF bed over the BA bed; it is newer technology and pretty cleverly done. But it all depends on how you sleep.