I found the way to order from Lazada, but their sizes very often don't match the description
This is the biggest problem I have with ordering almost anything on Lazada. Normally I will only buy things that are very cheap on there because there is a good chance that it is going to be too large or too small and then I end up giving them away to someone else.
Lazada has these elaborate sizing charts but then I think the person just throws whatever they can find into the bag so ship to you. The return process is more trouble than it is worth in most instances so I don't even bother. I live really close to a Central Festival that has a SuperSport inside of it but they rarely have anything in my size. Like you, if they have sandals or flip flops that fit me at all I will buy them provided they aren't super expensive.
RE: Finding shoes that fit westerners is not easy in Thailand