Dog hip harness recommendations

My dog is struggling with arthritis and progressive weakening of his hind limbs, making steps and getting into the car an increasing challenge for him. I was wondering if anybody has used those hip harnesses that can help support their backend. I would love to hear your good or bad experiences. And if by chance anybody has one they might be looking to give away or sell, let me know. My dog is about 100 pounds. Thanks so much. Meg