Most of what helps an aging dog's joints is unglamorous and free.
Keep them lean, because every extra pound is load on a joint that is already working hard. Trade one long weekend walk for several short daily ones. Put rugs or runners on slick floors, where most confidence is lost. Keep nails short so their feet land properly.
Supplements and medication have their place, and that conversation belongs with your vet. Mobility gear belongs in the same conversation, not after it has become urgent.