I've often thought it would helpful if the thing I was cooking on was close to as wide as the oven itself. In Australia ovens are usually 60x90cm. I often see and use American recipes because they're so common on the English speaking web and they quite often refer to sheet pans or baking sheets, which seem not to be a very common thing here. They look bigger than the types of things I can commonly buy here, which tend to be cookie pans that are really small. I used to think those American baking sheets were literally as big as the oven and slid in as racks but on further research it seems they're not actually that big and also need to sit on racks themselves and aren't as wide as the typical American home ovens.

I guess my theoretical baking rack would need it's rims to be less wide than the distance between rack grooves otherwise the food would touch the oven walls and baked goods that rise would might rise up to those grooves which would be no good either, but still that should only be a few cm. I actually sort of already have what I want as it came with the oven. It's a rack, that's not a wire and is a solid continuous sheet of metal that slides in to rack positions. The problem is, it always produced weird results when baking and seems to burn the bottoms of cookies and also has a large shallow ramp at the front that messes up what you can put on it. I read my oven instructions and discovered you're not actually supposed to cook on this thing and it's for catching drips. That's super weird to me since on occasion it's been used for this purpose accidentally and it's singularly unsuited to the task as any drips immediately bake right on to it and are impossible to remove and produce lots of smoke on the next use of the oven. I guess it's sort of better than nothing since I can theoretically clean that off when I take the rack out to clean it as opposed to the oven floor, but it's only marginally better since the effect of the baked on drippings is so thorough that it's near impossible to scrub off. Anyway, point is, while it's for whatever reason unsuited to the task presumably because of whatever it's made of and it's slightly odd shape, it's proof in my mind that the concept makes sense and can be done, and yet I can't find anything designed for this.

You can buy additional wire style racks, but seemingly not continuous metals sheets of appropriate size to fit in to the rack grooves.