Exercises that won't hurt my back?

I too have a back injury. Mine is my entire back so it varies if today mine will hurt more towards my neck or will it be the tail bone area. For myself I have found low impact exercises work the best. Avoiding any jarring, so no treadmill but the elliptical I can use but not for a long time. Yoga is actually limiting, but eventually you will be able to distinguish a good stretch from a bad stretch. Doing exercises that build up your back is ideal however they will start out feeling painful so only do a few reps. Isolating muscle groups is best however that usually involves specific machines. Doing at home can be very difficult and at home I stick to only PT that a doctor has prescribed for me and a begginer yoga DVD. Hope this helps!