Dress meltdown 😫😔

Hi all, we are having a short engagement and are getting married at the end of April this year. Budget is tight so can't justify more than around £500 on a dress. Obviously this knocks out most designers brand new so I've been looking at high Street and second hand on still white. I just dont know what on earth I want! I've ordered a couple from needle and thread to try but im afraid my h2b will just think I look like an old lady. I really am getting so worked up about this. Can anyone suggest anywhere obscure to look that I may not have? I like vintage style, definitely dont want strapless or mermaid, I quite like midi length, the plan is to wear green shoes. Im a size 12 and only 5 foot 3. Anything you can suggest to stop my brain from exploding would be great thank you!xx