We rent sleeping bags that are specially designed for cold temperatures in the treks and we offer sleeping bags for up to 5 ºF  = -15 Cº, In time you are booking your trek with us, you should request the sleeping bag if you need it, as at the spot it won’t be possible to rent it.
If you have one, make sure they are down and for temperatures up to 5 ºF  = -15 Cº,  or, even better,  made for colder temperatures than that –, you don’t want to be cold.