My first recommendation is to ignore CU when it comes to toilets. Their testing method on these things leaves something to be desired and often, field reports show their choices are sort of crappy. CU flushes, I think, sponges. The 'real' stuff is smoother and stickier. Manufacturers know how to make their toilets look good on CU's tests, but that doesn't always translate into real world situations. It's not uncommon for a recommendation this year to be an avoid the next when people end up buying them and then complaining about real world performance.
One-piece toilets will tend to be shorter than 2-piece toilets. One I like is the Toto Carlyle http://www.totousa.com/Portals/0/Pro...14114CEF_G.pdf which would meet your requirements. Someone with a small hand could probably deal with future maintenance, but it may be close. Toto happens to be the biggest toilet manufacturer in the world and makes many of its toilets for the USA (but not all) in Georgia with American workers. I have one, works great, looks great. Easily available repair parts (often not the case with Kohler), and inexpensive (available at Lowes, Ace, and most plumbing supply houses and hardware stores - try that with the Kohler!).
My second recommendation is cut off that counter extension.
If that's not something you're willing to do, then you'll have trouble with many newer toilets both getting them in, or servicing when the time comes. All toilets need some maintenance on occasion, and you not only have to have enough room to get the top off, you need to get your hand and arm in there to do things like replace the flapper valve. It gets kind of time consuming to have to remove the toilet each time that occurs, which is why my suggestion to get rid of that counter extension comes in. Your choice of toilets expands radically.