Size L - link says max waist size 70cm but I think it could fit quite a bit larger. Flat measurement is about 37cm across. The corset lacing is decorative, there is no shirring. 
I will also include a pinstripe putumayo capelet that I bought to coord with this skirt before I realized it didn't fit me. If you don't want the capelet just let me know.
I have a cat but he is not allowed near my lolita.