When Belle first started having trouble with steps (only going down them), I bought a used folding ramp on craigslist, and put it on the steps going out the side door. When I showed it to her she was really excited, and ran up and down it at full speed several times.
I'm hoping that Buddy's current situation is due to an injury and not directly related to old dog yet. I'm going to try to keep him from jumping off of the couch from now on though since that is a pretty big jump for a little dog who is almost to old dog...no sense in pushing our luck.