If using vegetables for this curry instead of the meat, try to use vegetables that will stand up to long, slow cooking without breaking down, such as carrot, parsnip, pumpkin. If you choose to use softer vegetables such as eggplant, zucchini or broccoli, add them in half way through the cook time.
Fresh curry leaves can be tricky to locate. I usually only find them at my local speciality Indian store. If you are unable to find them, just omit them.
Orange sweet potato is best for this curry rather than the yellow or purple varieties. The orange ones are much softer and will break down almost completely during cooking, giving the sauce a lovely thickness.