With today's toilet designs, an elongated bowl toilet often is very close to the depth of a round one, so don't use that as an absolute criteria. The tanks often don't have as much depth as the older ones. Toto makes some toilets using the Unifit adapter that can be used to replace the stock 12" one, but I think most of those are elongated bowls. If you go to their site, one of the selection criteria is offset, it will pop up all of their alternatives, then check back here if there is one you like the looks of to check performance.