Check Lazada to see what makes / models are available in Thailand & get a rough price. When you visit local shops then you’ll know what your looking for and if they don’t have what you want you can try on their stock for your size and then order from Lazada or online.
Exactly right, my wife recently applied for a renewal Thai passport & our daughter applied for her first Thai passport at the same time and both were collected the next day.
I’ve flown in & out of Thailand over 80 times and never been asked for proof of onward flight by immigration but the airline check-in desk asked to see my onward flight details several times.