Remember that thickness affects comfort. If your futon is just a spare bed for guests to use, you can select an affordable cotton-filled mattress that is 3 to 4 inches thick. If the futon is your primary bed, look for a mattress with inner coils or foam that holds its shape over time and provides more support while you sleep. Ensure the mattress fits the frame by carefully measuring its dimensions.
Shielding your futon with a mattress cover is a great way to protect your investment. Invest in a quality mattress cover made from heavy-duty cotton, microsuede or microfiber to give your mattress an upholstered look. Or, simply cover it with a regular bed sheet, especially if you only use it as a bed. For maximum protection, look for a water-resistant cover that repels stains.