I am suffering from SPD. I can't bear to be in my bed as turning is so painful. I even wake up with awful cramp.
SO then I hit on the idea of sleeping on an airbed to change the focal point of the pressure on my poor old body - hey presto!
We put a single airbed on one side of our bed and I've had two pain-free (almost) nights. It's MUCH easier to turn over because once you start turning, the air in the bed pushes you the rest of the way. Yesterday I had slight cramp in one buttock, this morning nothing and I'm much less stiff when I wake up.
Also, it's easy to get out of bed because the air moves you rather than your muscles having to do the work.
I'd say give it a go if you are suffering. An aibed costs about £15 (not a lilo), maybe less, and it's worth every penny.