The king mattress supplied in your Landmark is narrower then a regular king mattress. Approximately 4”, but regular king sheets work (unless your wife is like mine who absolutely hates the extra material). I know someone stated they had replaced their supplied mattress quickly, add me to that list. We tried for two weeks to make it work but finally bought one from Mattress insiders off the web. I was thinking about a topper, but figured spending $200 - $300 for a quality one and then finding it still do the trick (we are full timers) would just be a waste of money. Just my 2¢.