Are you needing to replace an existing unit, or installing an oven where there previously was none and are limited to 20-inch width? If replacing, how old is the unit? There are compact 20-inch wide ranges. Industry standards for wall ovens are 24", 27", and 30".

I’m trying to replace an existing unit. It’s probably 45 years old!

If nothing else works out, I use the Ninja DT 501 airfryer/oven. It's very functional. We never use the range oven anymore. Stainless steel interior is easy to keep clean. Link. It's 20.22" width is listed to allow for ventilation clearance. The oven is only 17" wide. It has the most interior height with 4 rack levels. I highly recommend this over competitive Breville and Cuisinart models with less space. Ninja does this by placing the controls in the handle. 110v.

I mostly want to bake in an oven. Is this too small?

You can bake most everything you'd use your old oven for. A 10 x 14 baking dish without handles fits as well as two layers of cookie sheets. It includes two racks, a screened basket rack and a pan with broiler top. If you buy it from Amazon, you can get free return if you can't use it. You may think you'll only use it like your old oven. We use it for many things almost every day. No micro anymore.