Hmm. Thanks for all of the helpful responses. It sounds like a non-custom slipcover won't work very well. The idea of having to make my couch every morning, or more likely every five minutes, with two jumping beans and one on the way to being able to move himself any moment now, does not appeal. How does one get a custom slipcover? Are there places online that make them?
The problem is, I haven't found very many couches that are really comfortable at all. I sat on one that's completely impractical. It's leather, expensive, and huge, but oh so comfortable. I know nothing about leather furniture, but I've heard that leather won't stand up to children. It also comes in fabric for cheaper, but I have no way to tell whether it would be as comfortable in fabric.
There's another one which is also comfortable, not leather, still pretty large, and I'd like it better if it cost less (wouldn't most things be better that way?), and then there's the one I asked about, which is a bit less, comfortable-feeling, but the display fabric is uncomfortable, and the other fabric, which has an extra fee in addition to not being on sale, of course, isn't amazing either.