When choosing a mattress on Amazon (especially during Prime Day), you'll likely be bombarded with ultra-cheap deals that can seem too good to be true — and that'd because they often are. So, when looking for a mattress on Amazon, choose a mattress thickness that's over 20cm (8") tall, as anything thinner will be totally unsupportive. We usually recommend 23cm (or 10") and above for most adult sleepers. Look out for the green "Customers usually keep this item" badge, which is a good sign that the mattress is of decent quality. Also, take a look at customer ratings and reviews, especially if the