I’m sorry, I don’t know any. But I’m sure there are many websites that have step- by- step exercises for the back and knees!😁
Hey my name is Luna, for stretching back and knees I recommend squats for your knees and for a stretch arched position would be a great back stretch! An arched position is where you lay on your stomach and have your hands on the ground straightened. This looks like a cat stretching. I hope this helped!
Always check with a trainer or doctor. But for me, when starting new, you will want to focus on body weight exercises like planks for your back. Then form for your knees, such as placing all your body weight on the heel when attempting a squat. Try this first by using a bed or chair. Sir then push off with using only your knees. This will lessen the weight on your knees and help with your form.