I have some of the same problems. Osteopenia, and some disk degeneration, and also arthritis in the L4-L5 joints, as well as spondlylolithesis, so I can relate to your pain and dilemma about surgery. My doctor only uses hardware, and I just have no faith in hardware being inserted into bones that aren't sturdy, so it's a big problem. Surgery isn't something to rush into at any rate.
About the PT, I tried it for 6 weeks and it was helpful I believe and if you can afford it and the time, I would say give it a try. I try to do daily stretches and walks and keep as flexible as I can.
Hope this helps. Best wishes