I made one for mine. Bought an old travel cot off ebay for a £1. It had a nice strong panel with a strong mesh inner, the bottom of which I Velcro-ed under the mattress. I made a little frame for the top from plastic conduit from b&q (about £3) which attaches to hooks in my roof.
I may be able to find a photo if you fancy / don't mind a diy solution.
If it really is to stop very young kids falling out in the night, then it has to be strong enough. Mine's a bit of a deterrent, and stops my pillows falling.