I just replaced the factory mattress in our new 179. I couldn't find anyone on line that had replaced there 179 mattress. So I will tell you what I did. Most of the replacements are 60x75. the 179 mattress is 60x74. I was worried about ordering one and it be to long. Because they come shipped vacuumed wrapped. Once you open them ,if you need to ship it back because it doesn't fit,it will cost you half the price of the mattress. I decided to go ahead and take a chance. I found a mattress that has a 25 year warranty,made in the USA. By a company called Brentwood. the mattress is there Bamboo 9 Queen short. 60x75x9 . I got it for a good price on an ebay store with free shipping. It fit perfect in our 179. Talk about comfortable. I have bad disks in my back,and I sleep wonderful now in the 179. I hope this info will help anyone like my self that wants to change there mattress,but wasn't sure about it fitting ok in there 179