I use the bed in my guest room for most couch-sized or smaller quilts. It's not perfect and because it's low, I have to take breaks to stretch. I pin the top edge of the back to the bedcovering (usually an older quilt), smooth the back out, leaving the excess to dangle over the edges. Then I smooth on the batting and the top. I slide a couple of cutting mats under the center and pin. I move the mats and, when the center is basted, I slide the whole quilt over to do the edges that were dangling down. This is tricky because you need to make sure the back stays taut.
If the quilt is big, I take it to a public place (library, church, etc.) that has a couple of tables I can use. They don't charge me for the hour or so that I'm there basting. My LQS also has tables in its classroom they let people use.