To begin with, I love the concept and practicality.  I have 2 recommendations 1. A pop up of the trundle would provide a full bed instead of a twin bed. 2.  Since it is a bed, the top is a mattress.  This style looks looks like a couch with arms and back.  With the mattress top, you lose the couch look.  I think an option of a coverlet of the same fabric as the arms and back would complete the couch look.  I have been looking for a twin quilt or coverlet for this purpose. Of course, an exact match will never happen.