I suggest, then, the 3 x 4 foamcore board. One can get really creative with the way they drape the unfinished top over and around it to see how things look. For borders and sashings, the size is big enough to give you an idea of what the quilt will look like, particularly if you put the corner of the top on the corner of the board. I have also used large pictures (hung on walls already) as something to put a half-finished top on to see how it looks, what will go with it, etc. Then there is patio doors, basement floors, the patio itself, a friend's place if they have a nice space to lay out a big quilt... you get the idea... the bed works, but only if you put a white sheet down over the quilt that is already there!
I finally got my own room for crafts when my SO and I moved into a 1700 square foot 4 bedroom house. I need to knock out the wall between the two adjoining bedrooms... not something that I foresee in the near future. I have too much stuff for a 10 x 12 room.
I see that you are the mother of a son in Iraq. My thoughts and prayers are with all our service people over in that unsettled area and with their families that are struggling with having a child there. Thankfully, my son did his hitch in the Army during the Cold War and was stationed in Germany.
Take care. Let me know how the foamcore works for you.