Hi K.,
I also used the floor, couch or bed. I used all 3 methods with my kids more than their changing table. Usually, it was way too inconvenient to go to another room to change them, especially since with my youngest, her room was all the way upstairs and the only time we were there was when we were sleeping.
You could get one of those cleaning caddies and load it up with all your diapering/changing materials for a few hours or for the day, whichever, and keep it handy to where you spend most of your time during the day. If using the couch, you could get a changing pad and store it under a cushion, for the bed, you know, slip it between the mattress and boxspring on your side of the bed.
Otherwise, the strap and one hand on baby always is the best thing I can think to tell you. You *may* be able to mount one of those rails that go on toddler beds on the wall somehow, but I don't know how well that would work.
K. W