Two plants I can suggest that I have chosen for my garden, are virtually unkillable, will grow in almost ANY soil or weather conditions & require little maintenance are: butterfly/african iris & Celtic Cascade tree. Both can be left to go a little wild for a natural look, or be cared for, to fit perfectly in a more formal garden. In regards to the iris, I removed my entire garden of mature, property damaging trees when I moved into my new house, but didn't want to wait years for a new mature garden, so I searched online for ppl selling/giving fully grown specimens away before they did renovations or re landscaped! The plants were a cinch to dig up, replant in my heavy clay soil & are thriving! I even cut some of them in half before planting and it didn't phase them!

Succulents and palm type plants are my go to low maintenance plants at the moment. I also have a plant called a 'zanzibar gem' that the tag said 'thrives on neglect' and they're not wrong! I water it once a month and its lush and green. This would all liven your space up with out you needing to maintain it. Have you thought about a ground creeper? They slowly cover your garden bed so it would be nice a green without you needing to maintain it much. Maybe add your climate to your post or in the comments so more people can help you out :)

Consulting a Landscape Architect or designer is going to be time and money well spent. Taking in the location and aspect of the yard. What you and your family want and how you want to use the space for, will help in creating the design. A good landscape designer can be found through you local landscape industry association and will be able to provide a cost estimate to construct the project. Then if you are going to get contractors to quote the work you will be getting quotes based upon the same brief and not random impressions based upon verbal interpretations which can only confuse your decisions. If your going to do this project your self then ask your designer how they would program the works and how to stage construction. Best of luck. Hope to see the finished job !!

Live in Seven Hills NSW. Budget is about $6K to $7K