OUr mattress is just over a year old. Been looked after as recomended (rotated weekly for 1st 12 weeks, then monthly thereafter) but has developed a line about 9 inches in from one side which does not pop out. First noticed it a month ago; it is still there despite the matress having been rotated and it is now on dh's side of the bed (and gets no use mon-fri cos he works away in london those days). Neither of us are especially tall or heavy.
Anyone else had this?