I am in love with my new day bed! It is great quality for the price and looks like it cost more than it did. I want to order another one in beige for another room and sell the one I got from Ashley furniture just last year!
I got an 8 inch memory foam mattress from Costco instead of a 10, so more of the bed shows, since the back is on the shorter size. A 10 inch would fit nicely, if you prefer a thicker mattress. I recommend 8 inches for the trundle.  You wont regret this purchase.