Hey Danny
I have been thinking about the same thing of late.
What I came up with, yet to be built, is a steel rhs frame the size of the bed mattress. 100 x 50 x 1.2 or 1.6mm. Some thin angle welded on the inside of the long runs and then pine slats lay across them. coat of paint.
Now for the fun. Bolt the frame into one corner of the bedroom at the appropriate height at each of the 450mm centre studs using hex head wood screws.
Then in the corner that is not supported run a balestrade cable from the corner up to the rafters in the roof. All done.
The you can put your desk or whatever underneath. Sleek, stylish and tight a$$. Is there anything else in life?
I could draw a picture