It is much easier and less stressful to order the gown true to your current size. Think of it this way; you can always take in a dress versus only having little to none to let out. Yes, taking in the dress may cost a little more depending on how much it needs to be taken in. But it will be nowhere near as costly as buying a new gown or trying to make a gown that does not fit – fit.
If you end up losing the weight and have to take it in – more power to you and congratulations on your weight loss! If not, you still have your beautiful wedding gown and do not have costly alterations. Of course the choice is always up to you on what size you wish to order. Best of luck!