Tofu/Paneer is usually added at the end of the cooking process exactly for the reason you described, not making it crumble. And instead of deep-frying, you can shallow fry the tofu cubes on a frying pan, just so the sides are browned. You could also air-fry the cubes instead to achieve similar browning. And since the tofu is already cooked after frying, you can add it at the end and give it a gentle stir to mix it in :)