I would suggest starting out with some day hiking and even some car camping. Nothing wrong with driving to a campsite, setting up, then doing some day hiking from camp. Sleeping on the ground might aggravate your back, so a good pad, such a Therm-a-Rest or similar inflatable pad would likely help.

There is a lot of lightweight gear around now compared to years ago, so check out some of the sponsored links on the site to see some of it. You don't need to go out and buy everything at once just to get started. A decent pair of shoes or boots, a small pack, a water bottle and perhaps a light jacket are the basics for day hiking on established trails like you would find in a local park.