If you start with a basic pattern that fits well it is possible to draft exactly what you want, but it is a skill. I'm not sure that software would do the job well. I've never used any myself, but have heard negative comments from acquaintances who have tried.

If you can find several patterns that together make what you want, you might do better with that. They don't need to be wedding patterns -- look at regular dresses and tops as well. It will probably be easier to work with one pattern company, since they would be using the same basic template for their patterns. Make a muslin to check for fit, and to make sure the pieces go together properly before you cut your good fabric. JoAnn's puts their patterns on sale from time to time at a reduced price. That would be a good time to buy 5 or 6 patterns that together do what you want.

Good luck!

Thanks, I will check out JoAnn's. I won't be making the dress myself, (I'm not that skilled!)but wanted to start the process. :)

When is the wedding? Who will be doing the sewing? Talk to that person - she may have all the answers.

I would suggest using different pattern parts from one company so they'd have similar markings. You can sometimes get old patterns at thrift stores; they can be smoothed out with a dry iron. Trace the parts on and make a 'new' master pattern.

When you make the muslin for fitting, try to use a fabric similar in weight to the good fabric so you'll have some idea how your design will drape. Cut with larger seam allowances for fitting.

We made my daughter's debutante gown from several patterns & she was thrilled with it. I agree with suggestion of trying to use patterns from the same company, but back in my years of taking various sewing courses, a size 8, e.g., will have the same sleeve curvature, hip width, measurements, etc.