About 3 1/2 - 4 months Kellie. How annoying that you're still having probs with the HAB! You can get an insert for your Ergo for your DS while he's still little. The new ones are called Heart to Heart and are heaps better than the older style one they had. Don't know if you really want to spend the extra $$$ though!

ETA - You could probably still bring a pram to the market, lots of people do, but I reckon you'll find it hard to get through the crowds!