If you can control yourself, it will definitely be enough.
What is cheap ah? Clothes, shoes, bags, hair accessories, ladies accessories and much much more, though those were what I usually haul back from my trip...
As for shopping in Pratunam:
If you are a small or average-sized lady, the clothes in Platinum Mall and surrounding malls should be the right place for your to shop (too many malls to count).
If you are a plus-sized lady, then go to City Complex (the one directly in front of Platinum Mall) and another shopping complex just next to it (forgot the name). The jeans are also cheap in City Complex. The alley between these two malls would lead you to the Pratunam market. Pratunam market got a variety of clothes for all ages (but no air-con and crowded, though prices may be a tad cheaper).
As for baju auntie and kiddie clothes, Indra Square may be a better bet. My mom loves shopping there and dislike Platinum Mall coz she complained that the baju there too young for her. Hahaha...
Oh, and the clothes at Pratunam are 'unbranded' ones. If you are brand-conscious, you should head to Central World or Siam Paragon.
I'm petite. Only wearing XS clothes. I went to Hatyai, but i didn't shop much, can't find anything good there.
Not sure bout BKK. Looking on clothes and shoes only.