Mawse; Sorry I'm not really getting what your saying. Do you mean that your only working one arm only? And/or, are you doing rehab now because of your pec & shoulder? Bands can be used quite a bit in rehab centers.
DB floor presses are a good movement, usually done on a heavy exercise mat. Can press the DB's together or alternate the pressing with each arm. If your doing one arm only, than you will be a bit weaker at first. Usually a training partner will hold the free arm down, while you press with the other. Or else grab onto something solid when doing this exercise. A lot of athletes train one arm at a time, can be an important method for sport training. Can develop equal strength (and size) and improve the general balance. Also can train each leg this way, for the same reason. Good Luck.