For someone with a bad back and still wanting to see wild animals, which parks in south Africa have the best (least bumpy/potholed)roads for viewing animals?
Of the few I’ve been, Kruger was the best maintained. I’d rent an suv if you want to use the well maintained gravel roads but the tar roads are excellent. Hluhluwe-iMfolozi, where you posted this, has good tar roads too, just not as many as Kruger. uMkhuze near Hluhluwe-iMfolozi, recently upgraded all of the park roads but the access roads were terrible. The KZN parks aren’t SANParks so they are not on the same website or officially affiliated.
It depends on where in S Africa you’re going. Addo and the Eastern Cape parks are pretty good too. Most S Africa roads are good. Traveling to S Africa will be more difficult than traveling in the country, except in some rural areas - in my experience.
As John says Kruger is good with tar roads being able to get you from one end of the park to the other, even being limited to these roads, sightings can be excellent. Your experience of course would be much enhanced by getting on to the gravel, and I guess you can try various roads, just turning back on any that are too rough. Some are quite corrugated, some just a little, some are quite smooth, it depends on weather and when they were last graded.
Only book into main camps, they are all fortunately accessible by tar roads.