I have read some encouraging success stories, and met runners using footwear modified to handle more impact. It is important to replace the action of those lower disks to avoid transferring the impact to the smaller disks above, and less shock absorption to the hips, knees, ankles, and feet below.
The problem with cushy footwear is that it tends to be inherently unstable. I've always been impressed with the continued development of new suspension technology that provides more stable cushioning, because the simple blown elastomers usually flex in all directions, and begin to lose cushioning with every use from day one. Unfortunately, the newer designs usually weigh and cost more. One exception to the weight problem I found was the Air 360 by Nike, which uses inflated air bladders that are actually lighter than foam, and fairly stable (barring an accidental puncture, of course). An extra caution with those is that the air bladders have been known to burst in the unpressurized luggage compartment of an aircraft. They may also have a harder ride than you may expect, despite the resiliency of the cushioning.
I recently saw a lady tooling around in a set of Z-Coil shoes, that took me back to when I owned a pair while coping with an injury. They have a steel shock absorber in the heel that compresses over an inch upon impact. Some runners have used them to rehab after fusion surgery, reportedly with great success. There is more orthopedically designed footwear in that market. The point is, you are asking more of the human suspension system you have left, so it helps to find a way to lessen the shock. Otherwise, there may be other impact-related injuries on the horizon.
Whatever you decide to do, honor your surgeon's advice to not "overdo it." Trails might be forgiving in spots and more of a shock in others. You will be tempted to progress too quickly with an entirely new lumbar arrangement. If your insurance can pay for it, I would highly recommend that you consult your physical therapist about the type of training you could do to prepare for a return to the road. You will probably be using several muscle groups in a different way than you were before surgery, and it is wise to make sure you are ready to shift that burden in an unfamiliar way.
Meanwhile, do an on-line search for "running after back surgery," and you will find several support groups for inspiration. Good luck with your recovery!