I quite like the boomerang pillow for along the back to stop that rolling back thing, and then a pillow between the knees.
Maybe a sciatic tendon stretching exercise before bed would help too?
I don't know how to describe it well in text but I'll give it a go.
Sit in a chair with your feet flat.
Bring one ankle up on your knee, keeping that knee centred (don't let it flop outwards).
With the leg that has the ankle up, drop the knee down as much as you can.
Put your hands on the arms of the chair. (kind of like as though you are going to use them to help push you to stand up)
Lean forward, chin towards that ankle and stretch as far forward as you can comfortably and you will feel the stretching. (it burns, but feels so good)
Hold for as long as you can, 10 - 15 seconds at least.
Repeat on the other side.
Repeat the stretch up to 3 times on each side if you can.
If you can manage this, it's a simple stretch but amazing. I've had hip pain for years and this is the best thing I've ever found, as well as the pillows. I get restless legs as well as hip pain if I don't do the stretches whenever my hips are playing up.
Hope it helps and makes sense!