Jackie... first Welcome!
As an FYI the 2020-2021 Horizon was a limited production model. It was manufactured at what was to be the NEW motorhome factory in Junction City, Oregon. The plan was to move all diesel motorhome production from Iowa to Oregon and the Horizon was the very first example to come from there.
However, mid-process Winnebago thought better of the plan and completely reversed course. They announced that 1) Diesel Motorhome production would not move to Oregon, 2) Instead they were closing the factory there and making it a Service Center, 3) Followed by putting the entire Oregon property up for sale and removing or selling off all of the equipment and molds, etc.
As part of this process they built a sizeable number of Horizons from the parts and supplies they had on hand. I've heard estimates from as few as 25 to as many as 45. Then they full-filled all pre-orders and shipped the rest to dealers all around the country.
After this the new Horizon model pretty much was discontinued.
In the end Winnebago had to build an entirely new diesel motorhome factory in Iowa and staff it with new employees. They developed two new Journey models to be built there, but it took them 2+ years to make that happen. It seems like these new Journey models are being delivered, but honestly there has not been a lot of evidence of that model in the marketplace.
We have seen about 2 or 3 Horizon owners here since 2021, but not more than that. So, the chance that another Horizon owner has investigated or actually replaced their sofa and is a poster here is awfully small. In other words, you a likely the only one to have done this project or thought about it.
If you move forward with the project please be sure to document the process and revisit here to post about how you make out.
Over on
www.IRV2.com (we're a spin-off of that site) you find a great many that have replaced a sofa in their motorhome. But again, due to the limited number of new Horizons you'll not likely see any direct examples of that process.
Best of luck, the Horizon is a beautiful motorhome!
PS. In case you are not aware... Winnebago had a sub-brand called Itasca that was closed in 2018. When Itasca was in operation they had a Horizon model for about a decade or more. These were models built to be a sister coach to the Winnebago Journey. You will encounter Horizon models much older than your "new" Horizon. Be aware that these are completely different than your 2020 Horizon. Almost nothing on the old Itasca Horizon is the same as your new Winnebago Horizon.