Good spa suites in Melb?

Help needed; I'm trying to find a good place in Melbourne that has spa suites (nothing like splashing around in a nice hot tub with some fun company...). Central CBD location or Southbank would be good but it has to be a decent sized spa, ideally accommodating 3 or 4 people. Based on your experience, what are some of the best places to stay for a night of bubbly fun? Thanks.