If you mean that you were cold and you want to keep using it for a while, the 'old tramps trick' is the cheapest way of solving the problem, newspaper pages under the mattress.
If you want to buy a new one, I only have experience of Thermarest products. Mine is a Neo Air, I find it very comfortable and to date, I've never been cold sleeping on it. It's not self-inflating (I use a low tech method to inflate it, a plastic bag pushed over the valve, rolled and the air squeezed into it) but if you want the self-inflating type the choice seems to be, their thin one or their thick one. I have a thin one a Prolite, its works well but for comfortable sleeping, I have to tweak the air pressure, too much air and it's like sleeping on concrete, too little and because I sleep on my side my iliac crest gets painful.