My garden desperately needs a makeover.. luckily my sister has just finished her horticulture degree and she is going to design me a gorgeous garden and basically do all the work for me.

You could try calling Melb Uni Burnley campus where they study horticulture, and try offering your garden free for a uni student to come in and design for you for one of their projects? You might still end up having to do all the work, but they might (not sure though) tell you what to plant and how to fix the soil etc?