you didn't indicate the style of canopy you'd like to create.
but it sounds like you feel a flat surface for the canopy is necessary.

http://www.mana… - with pictures!

http://www.sout… - a formal style

another option, put hooks in ceiling over corner points of bed, get some rope/twine/wire and hang a wood frame or PVC framework from those hooks so that the framework hangs parallel to the bed. hang your fabric from the framework.

http://www.nysp… - check out the 'secret hideaway'

http://images.g… - lightweight fabric options

http://images.g… - build your own
http://www.chia… - simple fabric solution

I would use small hooks from the local hardware store. Put them in the ceiling every 12 inches or so above where you want the canopy to hang.. If you are using some flimsy fabric like see through lacy stuff you can use smaller hooks. Now on the fabric, I used shower curtain circles, gold ones, and glued the material to the circle then sewed a few stitches around the circle to hold the material on. Take circle,hook it onto the small hooks in the ceiling. It was really cheap and I used white sheets I bought really cheap. I added some lace from the bargain bin at the fabric store. Very inexpensive, Like under 25 dollars for the whole thing..

What about an old parachute from the army navy store, you can dye it in a big washtub staple to the ceiling like an Arabian tent. just pouf it and staple then let it puddle on the floor Add a big tassel to center, cool. And the dye job can be sloppy , it is kinda tie dye looking