I took the initiative to find out for myself how big a Upper/Lower Interior room is aboard the Carnival Conquest.
I did not get much information from Carnival's official website. However, I went to Yahoo Travel and got as close as I could without booking a room for myself. According to them, the room size is 185 square feet. That is almost 25 extra square feet than what I had on the Inspiration. So, it should be comfortable enough for the two of you.
So, I hope you have a good time on your cruise