Thanks for your advice. Honestly, that optical shop tried to recommend some other expensive lenses to me at the beginning but I declined it. Eventually, I have chosen the cheapest one and the shopkeeper promised to make it slimmer (who knows).
The reason why I took the advice from Ocean X because I didn't have time to shop around and they told me that it will only cost around 2 to 3 hundred dollars. Anyway, It costs me HK$380 now which is .......