I'm a spanish android developer and I've got a friend with sleep apnea. He told me that he was using and Android app to sleep better, it helped to sleep to the left or right side. The app owner died... so the enhancements he needed couldn't be done. I have made an app with the same functionality and pubished in the Play Store. An american user has helped me testing so I can say a real apnea sufferer is using it. He says the app has replaced the CPAP machine.
I don't think this app can be a solution for everybody, but I'm sure it can help more people so if you want you can give it a try. Here is the link:
About the funcionality, the device starts vibrating after X seconds of an incorrect position (you can configure this variable in settings), and later if the user doesn't move it starts sounding in ascending volume. You can pause it for X minutes (go to the bathroom or whatever). The app stores the data of each sleep and you can see a chart with your evolution. In a Samsung Galaxy S7 it only consumes 7% of battery the whole night!
I appreciate feedback, it has helped me to make a better app.