I think you can do yoga purely for physical relief, and your mind will be okay. (I am a meditation teacher, and also do yoga.) In fact, yoga may help you to center and focus your mind, as you will be focusing on the stretching exercises and and how your muscles feel. You have been very honest about your situation and I appreciate that about you. I perhaps should not have used the word " weird" -- but rather, "unprofessional". As an example --- I go to the same dentist every four months for teeth cleaning and have not been able to afford periodontal Xrays for a few years. I explained this to the dentist. He said to just keep coming in for the cleanings, and it is okay for now. I know this is not his usual policy but because of my finances he is working out an arrangement. He did not make me feel embarrassed. Finances are a fact of life. Continue to be honest with yourself, and I think you will find all your answers. Best of luck, and such good news about your back!