Hi! From what I've heard, Dr Samantha Rachel Yeo is really well-regarded, mums say she listens patiently and explains things clearly, which is so important when you're making decisions about your care. I don't have direct experience with Dr Liu Jia Yi myself, but both should be solid choices if Dr Tong isn't available soon.
On the A1 ward question, it does get booked up, so I'd recommend confirming availability and perhaps booking early when you lock in your doctor, better to secure it sooner rather than later. Definitely worth asking the KKH admin team directly about current wait times too, since it can vary. All the best with your switch to private!