I re-read your question and now I have one. Were you serious that the toilet is only 18" from the floor to the top of the tank and is that a requirement? If the toilet is recessed under a ledge that limits the height, then I don't know what you can do without remodeling the bathroom. I know of no toilets regardless of price that are less than 23-3/4" and you probably don't want to know the price of that one. You will probably be in for some sticker shock if you haven't priced toilets recently, but try to remember this is a purchase that can last 70 years or more. My suggestion is that you go to the Home Page of this site, click on SHOPPING, then click on TOTO. Peruse the many options available as well the the specs for them. You should seriously consider ADA height. Remember too, these are the prices Terry Love sell them for and is not necessarily what other dealer may charge. Come back here if you still have questions, you'll find lots of us willing to advise you, perhaps with some bias, but sincere.