Do we need a topper as well as a mattress

Our current mattress is almost 20 years old, so we feel it needs replacing. We had planned to buy a Premier Inn Hypnos mattress after experiencing sleeping on them comfortably in several different Premier Inns, but came across your informative website and think we'd prefer yours. However, I can't seem to find out whether we need a mattress topper as well as a mattress. Also, as you describe your mattresses as 'two-sided', should they be turned regularly? Many years ago, my Father sold Vi-Spring mattresses and the vast majority of complaints about them stemmed from people not turning them, so I'd really feel happier if we can turn our mattress!