Other physical (samatha) meditation objects besides breath?

Does Buddhist samatha meditation allow for physical meditation objects other than the breath? I have noticed I feel much more contentment with the physical sensation of "back straight". Please give examples or references. Ayya Khema writes (Know Where You're Going) : > In the beginning we need the necessary meditation practice, the methods that will be our key to open the door, but within them we must find something that is of particular help to us. That element can be physical or mental, concerned with **posture** or with thoughts. > Upasika Kee writes (Pure and Simple): > Sit straight and place your hands one on top of the other on your lap. Hold your head up straight and keep your **back straight**—as if you had a yardstick running along your spine.