Folding Bed Tray Where Can I Buy A Tray That Arches Over My Bed? What Are They Called?

Where can I buy a tray that arches over my bed? What are they called? - folding bed tray

I want something that you may be able to store under my bed, and unfolded on the bed and when I watch a DVD on my laptop, or a breakfast tray on it or whatever. I know what you call these and where I can be a line or in a shop in the UK. Thank you!