having the same problem at the moment such unpredictable weather, I found a size 2 snugtime sleeping bag they have them in bigger sizes as well,I know they are not cheap I managed to find one in our local Harris Scarfe store for $20 but I don't imagine you have this store in Melbourne I think its just a Tassie thing and I think they just had them marked down for clearance.
They do have them listed on their website though not sure how much they retail for but I sware by snugtime now Paige has 3 bags in different sizes and thicknesses They will do a few more bubbas yet(except that they're pink!!)really good quality, sorry probably doesn't help much