I have the Leachco Back & Belly (in the US). It's a giant horseshoe like another that was posted on a previous page.
I really love it, but I find that I can wiggle between the sides and still end up sleeping on my back sometimes! However, I usually have some part of my hips on the edges, so I'm not flat on my back, which I'm pretty sure is better.
Worth noting that it's gigantic. If you share any bed smaller than a king-size, your partner will find him or herself utterly squished.