Today, choosing a futon mattress can be a bit challenging. While it used to be that you didn't have much choice in the mattress, today you can choose from different sizes including twin, full, queen and even chair and ottoman sizes as well as different firmnesses is such as soft, medium or very firm. Not only that, but you can have them with coils or just foam and in a variety of thicknesses ranging from 6 to 10 inches.
Today, most mattresses are made of cotton and foam - the more foam, the firmer the mattress. A 6 inch mattress will provide you with adequate comfort for almost any futon frame and may be the most convenient and they will be the lightest. Thicker mattresses at week to the frame and also are heavier for you to work. However, if you want the most comfortable sleeping you want to get the firmest mattress as this will help reduce motion transfer when more than one person sleeping in the bed.
Perhaps the most important thing you can do when choosing a futon mattress is to simply try it out! Don't be afraid to lay down in the, change it from a bed to a sofa and sit down on it. Depending on your intended use of the futon, you'll know whether you require extreme comfort or not.
While most mattresses look pretty similar on the outside, they differ on the construction on the inside. If you cut off a corner and looked at the revealing layers of the mattress you might be rather surprised. You'd probably find that a lot of the mattresses have foam in the middle surrounded by cotton on the outside and then of course the mattress fabric. Other mattresses for your futon may have quail springs inside surrounded by foam. These inner spring coils can be different amounts of thickness too.
While you may have to take the frame into consideration, choosing a futon mattress is simply a matter of personal preference and budget. The more comfortable mattresses will cost more, however they may also be better made and last longer. Either way if you take care of your mattress you can expect to get about seven years out of it.