It is an awesome mattress. It is 4.5 inches think and is as described.
The mattress fit perfectly in the sofa. As for it being memory foam. It is very comfortable. Molds to ones body and less pressure on joints and muscles throughout the night.  Mattress comes with a high quality mattress cover. Just a suggestion to anyone that purchases this item. Being memory foam. As soon as it is delivered. You will want to air it out for about three to six hours before installing into sofa. It does have a smell that will last for about a week. Everyday the smell lessens and after one week the smell is gone. Vey happy with this product and would purchase again in the future should the need arise.