Convection oven

Susi,  sorry, I don't know much about commercial ovens, though I have a Roberta as well, but I might be able to help a little.  The heating element for the Cadco is not actually in the baking chamber, it is behind the baking chamber, so even if you could turn off the fan, you would not get any heat in the oven.  For a company to offer a convection oven with the ability to turn off the fan, it needs to have an element either in the oven cavity itself, or at the bottom of the cavity with a shelf covering it.   Don't know how commercial you want to go,  but Pleasant Hill Grain carries the Rofco line of ovens  https://pleasanthillgrain.com/rofco-electric-stone-oven-b20-bread-oven    there are a few models, but all do the same thing .  Basically, there is a heating element at the bottom, or the bottom of each stone, then a large stone to retain the heat, and a vent on the front -  when the vent is closed, if the oven is fairly full, you will get the same humidity that you would in a dutch oven, and then you can open the vent to let out the moisture.   It gets pretty good reviews.  There is also an accessory called a steam tray, which sounds like a heavy piece of stainless steel, you add water to it and place it in the oven and it generates steam.

  There are some commercial ovens that use a similar concept,  like the Bakers Pride electric ovens -  many are pizza ovens with a very shallow deck, but some offer a decent size - this has a 7 inch height, would should be fine for most loaves  https://www.restaurantsupply.com/bakers-pride-bk-18-electric-countertop-bake-and-roast-oven-1700-watts/ .   They have a much thinner stone - probably half an inch or less, compared to the Rofco which is nearly 1 1/2 inches thick,  and probably will not seal as tightly as the Rofco, and don't have a vent like the Rofco, but again a similar principal -  heating element under the stone, and no fan. 

Forgot to mention, as you go up in size from the Roberta, if you stay electric, you will likely need to consider the power requirements of the oven .  The Rofco's all require 240 volt line.  You may not have a spare line in your house. As you get even bigger, you see ovens that require 3 phase service, which is not available in most homes.  Also, check on the fire safety issue.  Many commercial ovens require a certain about of fire resistance in surrounding materials and certain amount of open space to operate the oven.