Which part of SA are you going to? It's twice the size of France and has thousands of miles of great surfing coastline! :D
If you are going to Cape Town then a 3/2 fullsuit is essential all year round; even False Bay on the Indian Ocean side gets cold. Should still be plenty of swell, with the South Easter (wind) making itself felt. So head for the Atlantic side around Long Beach and Noordhoek for chilly offshore barrels.
Southern Garden Route and J.Bay/Port Elizabeth area you'll get away with a shorty in October, although the best swells are usually gone after September. 400 miles of fun beach breaks to choose from if J.Bay is flat/blown-out.
Further east towards East London and Durban is shorty surfing and baggies. Get up early to get the offshore breeze before it goes onshore around 11 am.
Enjoy your trip and remember to be respectful of locals, particularly at places around Durban (Cave Rock) and Cape Town (Glen Beach & Kalk Bay). 8)