I would say that yes, you do need a/c in the bedrooms and living areas. Temperatures can reach 40+ degrees in Perth in the summer and without a/c or at least a fan, it'll be impossible for you to sleep.
Most new properties will have a split a/c or reverse cycle system, which enables you to heat up the house during winter and cool it down during summer. If you can, look for house that have reverse cycle running a/c running on gas as those running on electricity can be quite costly to run, especially in the summer.
Failing that, buy a few fans and makes sure that the windows have a security screen on them as you will need to open them at night if you have no a/c to at least let some cool air inside.