(Image credit: Future) A mattress is quite the investment, but your purchase can really pay off if the mattress you choose is built to last. However, as beds come in a variety of designs and prices, it can be tricky to figure out how long a mattress should last. That's why we've created this comprehensive guide to mattress lifespans, exploring how long you can expect your mattress to last based on its type and price tier. In this breakdown, you'll find the life expectancies of the best mattresses and most popular designs – including memory foam, hybrids, and the classic innerspring – and how their price tags can influence their durability. Key takeaways: at a glance Swipe to scroll horizontally Mattress Lifespan Why? Innerspring 5-7 years Springs and thin comfort layer wear out easily, causing sagging, discomfort, and creaking.…