@NEPatsGirl , I’m going to give some comment/advice that will not go well with everyone here.
Many people here on CC and in real life are all about the formal, glitzy wedding experience. They love it, enjoy it and believe it is or should be standard protocol. It works for them and that is 100% fine!
I am you. A long dress and glitzy shoes and any other bling would be like putting me in a clown suit. Totally awkward, the opposite of my personality, a waste of $$$ and not a confidence builder. I would be SO uncomfortable and unhappy - it would not make me feel special or happy.
That isn’t to say I don’t like putting on a dress or a pretty pair of shoes. I wear dresses nearly every day to work. I like quality shoes but they are not heels, they are not sparkly.
My S and DIL knew this about me and without hesitation told me to choose a dress that I loved and made me feel good. When I found a short dress (black and white, sleeveless, above the knee, a little flowy, just a little sparkly near the collar) I showed it to them as a possibility they were fully in favor. It was dressy in a fun, not stuffy way. Oh, that describes me so perfectly! It was ME. I loved wearing it. I still have it and would wear it again. I’ve watched the video of my S and me doing the mother-son dance over and over again (it too was very untraditional - a really fun upbeat song that has meaning with me and my kids from when they were little) - and it looks not out of place at all! I danced all night in that dress and my simple black sandal that had a 2 inch wedge heel (which I recently sold because I haven’t worn them again since the wedding going on 3 years ago - 2 inch heel is not my daily choice!)
The MOB chose the traditional long dress with a little bling. It’s what she wanted. Our pics look just fine. It’s not like I was wearing lime green! 
I think you should have a honest conversation with your S, FDIL, MOB when you’re together and run by what you’re thinking and be honest about what is YOU. Surely you can find a compromise!
Choose a dress that you can’t wait to tear off the hanger and put on. That you will beam with satisfaction and self confidence when wearing it. It’s a dress. A dress for a moment. When you look back at the photos I want you to think “Damn, I loved that dress!” not “Ugh, that long formal dress was SO not me”.
And you have plenty of time! You’re find the perfect one. 