RooMama, I've used Rimadyl for quite a few of my seniors, and none of them had problems with it. If you've already noticed improvement on it, it may be worth continuing, but I'd also talk with the vet about taking Zantac, Pepcid, or Prilosec concurrently to try to decrease the risk of gastritis or ulceration. Of course you want to give it on a full stomach too.
I've used tylenol #3 for most of my osteo dogs with good results, if tramadol no longer worked. There are more potent narcotic pain meds, but then you have to weigh the side effects (sedation, loss of appetite, etc.) vs the benefits.
Have you tried acupuncture and/or chiropractic?
Teddybear sounds like a brave little sweetie! I hope you find a way to keep him comfortable and happy.