I'm replacing my Cal-King mattress.  I was wondering if it would be a better idea to stick two extra-long twins together and put a cal-king size topper on it so I wouldn't feel the crease in the middle.  The reason why I think this might be good because maybe the size of the king mattress causes there to be more sag in the middle as time goes by.  Maybe the narrower twins won't sag as much because there would be less width for sagging to occur?  Can anyone help with this decision?