There's plenty of spots to launch onto Georges river (which I guess you know is the downstream section of Woronora River).
The boat ramp at Como would be fine. There is a rowing club there every morning, so it can't be too bad. Not sure how much beach at high tide, so might be straight off the boat ramp for those times. (Probably better considering the gooey mud that constitutes sand in the Georges River.

) If you go here, paddle straight across to Neverfail Bay and say g'day.

There are also some easy spots to launch on the St George side, at Kyle Bay and Connells Pt sailing clubs. (Sandy beach, but not nice white sand like Port Hacking.) You can explore Oatley Bay, etc. Otherwise just on the northern side of Captain cook bridge you can easily launch at St George Sailing club, or Kogarah Bay sailing club on the northern side of Tom Ugly's bridge to explore Kogarah Bay & Carss Park.
Don't forget about the illustrious Sylvania Waters. A couple of boat ramps around there (just west of Captain Cook bridge on the southern side) with sandy shores or pontoons (google them), and you can explore the man made canals for something different.