My DH actually owns a sofa bed shop (I wont advertise that), but the main stockist he uses (http://www.innovationliving.com.au/) stock elsewhere around Australia too, and they may have something suitable. But then again they may not. They are a little different than usual. These ones are also mid to high end so depends what you are looking for as the can be $$$. But in their range there are ones that are for 'everyday' sleeping (ie sprung mattresses etc), and those that are more for occasional use.
In the past we have also owned a Molmic brand one (which is a conventional style trifold thing), and it used to be great nd super comfy, but at 10yrs old it really is not comfortable anymore for sleeping (great looking sofa though)
The other option, if you are happy with your current sofa/ don't really need another one, would be something like an aerobed?
OP, just saw you are in Sydney - I think there there are 'Mastersofa' and 'Sofa bed specialists' who sell them - but I don't actually know what those shops themselves shops are like.
(Mods, if this breaks any of the rules, please delete and I am sorry)
This post has been edited by mrsboof: 27/11/2012, 11:16 AM