Any paving or concrete being a thermal mass with retain the heat. Maybe a permeable spaced paving like Adbri Turfgrid or similar. A quality hardwood decking is a classic but may or not suit your house style. Bluestone is a great look but shading would be worthwhile to keep the heat out of it if it's what you really want and it suits the house.

Your plans seem expansive and maybe costly. Id spend just a bit more and get a proper professional plan done.

If this was my place, I'd definitely install a skylight (even just a DIY solatube which someone suggested), then depending on budget I'd make these changes:- - replace floors with light colour timber floorboards since they never date - replace furniture with light colour furniture in both lounge and kitchen - paint kitchen and hutch white - add some plants in white pots - go for large light coloured wall art - replace curtains with roller blinds to maximise light I love the bluestone - it will look amazing when you've added some lighter colours to the room!

I believe CDK Stone in VIC sell it by the slab, rather than tile. Off the top of my head I'm not sure of anyone in Sydney.