Any beds that come with a mattress will have a section of the description explaining the type of mattress.
For example, Divan Beds will come with a mattress and explain this in the description and Divan Bases do not have the mattress in the description.
This is the same with all the products on our website.
If you are not sure please contact us using the live chat icon on the bottom right side of our product page and we will happily let you know if the product you are looking at comes with a mattress or we will recommend a mattress if needed.