I've SI joint issues on one side that my chiro has been working on. I've also been experimenting with finding different sleeping positions so I don't sleep on my side so much (probably a futile effort) as I've hip bursitis on both sides. I've been noticing that when I try to sleep on my back that it helps a lot to elevate my feet 4 or 5 inches at night. This really makes little sense to me, but there it is. I can't sleep with anything under my knees, but apparently elevating my feet is different. I thought I would mention it in case it might work for others. I do have a new mattress that certainly helps - and am trying to train myself to sleep with something between my knees when I am on my side which is my preferred position.