Hi Clair. Many blessing to you and your son on your upcoming nuptials. You must be truly excited!
Here is a link that will help you decide:
Best of luck to you all.
Lavender is a beautiful color and will look very good on you. There are many styles that are tasteful and conservative. If you are concerned about the weight issue, I would avoid a "suit" as most are form fitting and man-made fibers. Keep to the natural fibers (cottons, woven linen's) as they breathe better than the man made fibers. If it is a blend, (cotton/poly), look for a much higher percentage of the natural fiber, it won't wrinkle as much and will also still breathe. Make sure your "unmentionables" are also natural fibers (slips, etc). No hose and open toe shoes will also keep you from overheating (treat yourself to a pedicure!)
Good luck on your shopping expedition!
Mother of the groom dresses
Then click images instead of web for the results and you will find a lot!
You can add lavender or cream to the search bar as well.
Here's an example. Not sure if it will work for you.
This search is for lavender mother of the groom dress
The good news is, hardly anyone pays any attention to the mother of the groom!
As long as it's flattering and a bit dressy...whatever! (And, I wouldn't be railroaded into wearing lavender unless it suited me. Personally, I find all shades of purple depessing.)