Obviously I am not familiar with your particular details...but I just wanted to mention that many insurance companies are no longer authorizing payment for a spinal fusion if the only diagnosis is DDD. There needs to be proof of spinal instability, or evidence of nerve compression. Performing surgery for pain relief is no longer considered an acceptable condition.
In a way this makes sense as various studies have shown than fusion is not statistically successful when a patient's major pain is in the back. It can help some people, but the percentage is not high. It is much more effective when the patient's primary pain is in one or both legs (often the result of nerve compression).
I think we all struggle over the decision of whether to have spine surgery, or not. Very seldom is surgery ever an emergency (except for the reasons you mentioned.) So there is usually plenty of time to agonize over the decision. I know I did. Most people will tell you that you'll know when the time has come...and probably that thresh-hold is different for each of us.
I met a fellow spiney in the lobby of an alternate therapies clinic one day. We started chatting...I was wearing my back brace and had recently had a 3 level fusion. I told her that my world had become so small that I was basically housebound....she looked at me incredulously and asked why I hadn't purchased a wheelchair so I could go do the things I had told her I had wanted to do, but had not been able to do....She said she would never have surgery as long as she had someone to push her around. Obviously, my time for surgery was different from hers!
My point is that this is such an individual decision. Only you will be able to decide when the time has come...if it comes at all. I have read that DDD actually improves as the patient ages...so if you don't develop any bad nerve compression, perhaps you will be able to avoid it altogether, OR, you can wait until technology comes up with something better.
You should try to figure out exactly what you would accomplish by having a fusion, what can be done to control you pain if you do not have surgery, and whether you can live with things the way they are.