Do you need a shelf or just think a shelf would look good?? With your heringbone subway tile pattern, very interesting actually, you've really ruled yourself out of putting in a shelf and not interupting the tiles to such a degree that it would most definitely detract rather than enhance the wall, so I agree with myperfectadvice, leave it as it is, as it's a beautiful design and kitchen from the little I can see and the pendant light is stunning. BUT, If you are desperate for a shelf and your kitchen is black/white then I'd go metal and 50mm thick and if you have timber doors and or floors, then I'd go timber for sure, again 50mm thick. I can't see the cupboard doors but I can see a timber knife block on display, so I'm guessing you have timber??? Good luck. Cheers, Barbara

I love the colours you suggest and they would really make the corner pop. Make it personal. Be brave. Options; Wall mounted boxes or floating shelves to display some colourful treasures above toddler height. Pinterest search 'Wall display Boxes" The next 2 sound a bit hippie but you can do them with your toddler and if they get pulled down noone gets hurt. - Fabric collage on a sore bought canvas with pieces of velvet, satin, silk in your favourite colours. Finding some vintage fabrics or op shop clothes to cut up is a cheap activity and add you can even add some bling or go with a geometric art deco style.Again Pinterest has great images. - Patchwork quilt style wall hanging eg.https://www.instagram.com/jenkingwell/?hl=en

can you post a photo of the heater?

They are most popular in temperate zones like Southern NSW & Victoria. You might struggle with humidity in Sydney and conifers. But the best people to chat to would be these people who can help you with selection and give you a realistic idea whether the intended plants would struggle in your climate. https://conifer.com.au/ The diosma's may be a bit more amenable to a Sydney locale since they aren't a conifer, but look very similar to one. They are a south african native and like so many other SA plants thrive in our local conditions and in the heat. Here is a blog about diosma. They are indeed a very pretty evergreen that prunes well into a nice low bush. https://thelinkssite.com/2013/05/26/diosmas-a-very-hardy-plant-for-your-garden/ If neither of those work there is a native with a similar appeal, it's a weeping wattle that might be just the ticket. I've seen this plant used to beautiful effect in cascading gardens and rockeries. It comes in several varieties and one a very bright lime green for a splash of colour. They flower too. https://www.nurseriesonline.com.au/plant-index/australian-native-plants/acacia-cognata/