Developing a program for yourself


I'm new to yoga but I've been training in Martial Arts all my life. I'm in my late 40's, and have some medical issues with back pain, knee pain, and arthritis to name a few. There are tons of programs online like Yoga International, DDP yoga, and others, but how do you know what's best?

I'd like to practice at home, but I want to do it right. Is there a program I should go through, or is it just as good to look up "Beginning Yoga for back pain" on youtube and do them? My wife takes a class at the local gym, and I'd like to do it at home. Do classes have a set program that they do, in a specific order or do they basically do the same thing each week? How do I begin and find a program for me?