Just come from KMart
https://www.kmart.com.au/product/single-self-inflating-mattress-42498575/
Self inflating Sleeping mat $22 - bit thin at 40 mm, bit heavy at 3 kg - would do at a pinch
https://www.kmart.com.au/product/altitude-hooded-sleeping-bag-42890546/
Sleeping bag pretty good at 1.2 kg , $45. rated down to 4C
https://www.kmart.com.au/product/ridge-sleeping-bag-43491162/
Sleeping bag pretty good at 1.9 kg , $49, rated down to 0C
https://www.kmart.com.au/product/thermal-eva-foam-bed-roll-42305880/?srsltid=AfmBOor0fR9gjiJY05kxk7taXClRkkOG798Fx5PbQHnlGV8DrA4yEI_c
Closed cell mat $15 - bit narrow but again OK at a pinch. You can purchase this stuff, foil one or both sides, from insulation suppliers, I think up to 8mm thick - make it whatever size you want, supply you own packing straps.
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