I Like this slip - if you are losing weight, size down.  I originally got a medium, then one day I was wearing it to work, and it fell off, right to the floor!  I sewed the top tighter, but then it could be seen through the dress, so I just ordered another one in small, and it fits much better.  It's stretchy, so I think I could have worn the small before and been fine.  For reference 5'2" and I was 140 lb. now 122 lb.