This is used in our Project Room and can serve for sleeping if additional guests visit at same time.  We got an extra thick futon for the lower section in case adult guests need to use it.  The upper bunk cannot take an extra thick twin mattress or it would be higher than the security railing, comfortable enough for kids though.

One improvement we will do ourselves and that is to place a solid platform between the upper mattress and the slats the mattress lays on in order to keep the sheets from hanging between the slats making for an unsightly mess above the heads of those sitting or laying on the futon below.