I agree with a slow approach in increasing exercise, plus approval from your vet. That plus a very strict low calorie diet
Last January I lost my Shepard/Lab, she was 14. She had HD, a heart murmur, funculosis that almost killed her(severe body infection that took meds twice a day for 2 years), a food allergy that almost killed her, and who knows what else. All of this after she was hit by a bus just before I rescued her. She never had surgery for anything.
I started to exercise her daily, sometimes twice, when I got her at nine months, she loved to chase tennis balls and fetch sticks. All of this in addition to two daily walks totaling at least 60 minutes.
As she aged, she gradually slowed down and eventually didn't want to fetch. She did always look forward to her twice daily walks, no matter how cold or hot it got. In fact, her last day she wanted to go for a brief walk.
I have always attributed her long life to superior hypo allergic food and exercise, my vet agrees.
Anela