5-7 years doesn't seem like a particularly long time in the context of the life of a mattress. My (limited) understanding has always been that mattresses are the sort of thing many people hold onto for decades. In that context "it'll be good for five years" doesn't sound reassuring.
If you're positioning your product on price, you could make the counterargument that with your mattresses people could afford to replace them much more frequently than they typically do, of course. Just pointing out how this marketing point would strike me, if I were a potential customer.