Place a complete bed using /setblock
Solution 1:
You'll need to use two commands; one to set the foot part, one to set the head part. To setblock the head part of the bed, add 8 to the dataValue you used for the foot part.
For example, these two commands will create a bed facing north:
/setblock 0 64 0 bed 0
/setblock 0 64 1 bed 8
Or these two for a bed facing east:
/setblock 0 64 0 bed 3
/setblock 1 64 0 bed 11