I have put 2 Kohler Santa Rosas at home. Thefirst replaced a 2 piece with a broken tank, and the 2nd was after a wax ring failed on the very low toilet on the 1/2 bathroom.

They are 1 piece, 1.28 gpf and work well. Good height and install easy.

Kohler Santa Rosa

Got them at Home Depot and Lowe's, just look around for the better price. ~$280 or so.