For a long time when I had bad lower back pain and sciatica i would use ordinary pillows under my knees or between my knees when trying to get to sleep to help align my spine better an ease pressure on my back.
The pillows worked pretty well I have to say - until that is I wanted to move position or got up in the night or when they slipped out from under me and would wake me up!
So I had to look for an alternative and found that there are full body sleep pillows.
They are designed to put your neck, hips and spine into a better alignment , taking pressure off the spine and giving you a comforting , cradling experience to hopefully become more comfortable and enable you to drift off to sleep.
Sleeping with sciatica is certainly a challenge and if you get sleep , when you are asleep you are unaware of your posture and can wake up with a stiff neck, aching back etc but these body pillows basically deal with that so you retain a better posture all night.
I really do think they are worth it. I know I am a bit of a bear if i don't get a good nights sleep! If you are part of a couple if one of you does not sleep the other one often gets a poor nights sleep as well and it really doesn't help matters!
The only downside I can see in these sleep pillows is that they do take up room in the bed - but it really is a tiny thing compared to the benefits.
Its a personal choice which type you like so have a look and see what you think.