I have an inflatable bed rail that I use on my daughter's bed. It has a large elastic strap that fits under the mattress. The rail part is a long tube, maybe 12" in diameter, with a fabic cover. It has kept my daughter in her bed! I have found that the standard rails are too short for today's thicker mattresses - barely comes above the mattress! I don't remember the name of the product I have, and I got it at a thrift sale. But you may be able to find something similar online. Good luck!