The only space I have is in a cupboard stored vertically, but they’re clumsily leaned against one another other.
UPDATE: Thank you for the suggestions everybody! I ended up finding a metal thing, almost like a file organizer, from value village for $2 that worked perfectly.
There are racks you can buy in the kitchen section of many stores designed for this very task. Have you tried any kitchen stores? Bed Bath & Beyond was the obvious choice here in the USA, but they went bust this summer.
You can also 3dprint this if you or someone you know has a printer. There are a few designs on thingverse, or you could design your own with some CAD software for specific dimensions of your baking sheets. I printed one a few months ago for my cutting boards.