While normal beds are designed chiefly for sleeping, daybeds are designed to be used for sitting or general lounging around. Daybeds are usually placed in areas where you entertain, such as the living room, and use a metal or wooden frame with one side open. They look like a cross between a bed and a sofa, which is essentially what they are. You can use a daybed for chilling out during the day, then you can remove the pillows at the back to make it into a bed for anyone who wants to stay over.
Daybeds will often come with the mattress already included, but you should always look into the type of mattress the manufacturer has decided on before you make your final decision. Sleeping on the wrong mattress can cause back pain and lead to a poor night's rest, but choosing the wrong mattress for your daybed can make sitting uncomfortable, and that mattress can wear out faster if it isn't up to the task.
Firmness and thickness
Many people like to sleep on a nice, deep mattress, but added depth isn't usually as beneficial when you're sitting. Sinking down too far can feel a little uncomfortable, so it's best to look for a mattress of medium firmness for your daybed. At the same time, try to find a mattress that is relatively thin. A mattress as thick as the one you use for your bed might look a little odd on a piece of furniture meant as much for sitting on as for lying on.
The right filling
Spring mattresses work well for sleeping since the weight of your body is distributed evenly across the whole surface. However, spring mattresses tend to wear out quickly when used for daybeds since sitting places all of your weight across one specific part of them, and you'll soon find the front of the mattress becoming less supportive as a result. Additionally, spring mattresses tend to be quite thick. Instead, look for either latex or memory foam mattresses. These will prove more resilient to localised pressure, and they tend to be thinner.
Most people have succumbed to the temptation of a midnight snack or breakfast in bed at some point, but, generally speaking, the bed isn't a place where you tend to do most of your eating and drinking. Daybeds, on the other hand, are often used in entertaining rooms. Whether you're eating in front of the TV or having some friends over for a glass of wine, your daybed's mattress is going to be at greater risk of staining than your bed's mattress, so pick an option that is covered in a stain-resistant fabric.