You would likely need a large or XL depending on the brand's cut, etc. I would suggest trying the clothes on or ordering from a provider who allows free returns.
Very low-cut pants don't stay up very well. Your hips are the widest part of your body, so pants need to be relatively tight to stay up. This "tight" area...
I say you should use only one, especially if you don't have enough money for two. Just wash them thoroughly after every use so your makeup doesn't mix!
