I'm a maggie bride too and tried on a size 8 in the store which actually fit OK BECAUSE of the corset back.... I ordered it in a 14 though so I'm sure you'll be ok with the sizing!
back to the white issue: First of all, I think you'd look gorgeous in white, and its saving you almost 1000 dollars which is pretty damn amazing. Second, If you love the ivory touches on everything else, I would leave them and that way you get the best of both worlds. It may just be that i'm unobservant, but I don't think I would pick up on that little difference if I were a guest.
Being that I'm a bride too, I know how the difference can drive you nuts! I think it might be cute to have both themes though, thats just my opinion
Good Luck and congrats on the awesome find! hope you are feeling better after your surgery. Random side note: my brother had brain surgery for a tumor on his pituitary gland when he was 11. He's had no natural hormone function his whole life so we have constantly dealt with hormone replacements He turned out pretty amazing and I'm sure resolving the issue entirely is a weight off your shoulders!
XO
josie