(Image credit: Future) Clocking up enough time in bed but struggling to get comfortable, only to wake in the morning with neck and back pain, is frustrating. And it’s a sure sign that your mattress is to blame. Mattresses last between six and eight years on average, with that lifespan dropping off further for cheaper models. On the flip side, quality mattresses crafted from durable materials – such as luxury organic latex mattresses – can last for more than 15 years. Plus, how well you look after your mattress can make a big difference to how long it lasts. But the bottom line is that even the best mattresses on the market have an expiry date (yes, even those with ‘lifetime warranties'). Your mattress won’t suddenly stop being comfortable overnight. Instead, it’s more of a gradual tapering-off of comfort and support. How long does a mattress last?…