Managed to track down some insulation today. Big thanks to Gary at Right Homes for helping me out with this. Gary and Anna built my house. Great builders, and also just beaut people. Even six months after the build has finished, Gary was still keen to help me out.
Gary recommended that I use rockwool insulation in the wall cavity of the house as a way of maximising the effectiveness of its passive solar design elements.
This product is also spot on for insulating the oven. It's made from a mixture of rock and recycled building material. It's non-combustible and will withstand temps up to 650 degrees.