Hi there louise,
May in Perth is a bit of a lottery weather wise but viewing can be great.
One of our local public observatories is the Gin Gin Observatory just to the north of Perth.
http://www.ginginobservatory.com/
Also as fellow IIS'ers and ASWA member (me), we extend an invite to you to come to our dark sky site (home) on the outskirts of Perth in the hills for a bit of viewing through our gear.
Whatever occurs I'm sure you will have a great time.
