OP, @owlpassport has given the best advice on this thread. And she's right about the Jolie Moi dress - sorry ... It's also not just polyester, but polyester mesh! And is very dowdy IMO ...
Also, you said you're quite short but big-busted - & some of the dresses posted on here I think are the worst possible styles/patterns you could wear!!! Some are decidedly frumpy, some are only suitable for graduation balls ...
I would look for high-quality but ready-made, which you can have tailored perfectly to fit. I have rarely (never?) seen something made by a dressmaker that doesn't look it, unless it's at couturier-level.
Why don't you, to get yourself started:
- Find out what colour the bridesmaids will be wearing asap. You don't want to find out they're all wearing, say, azure chiffon when you've just bought a dress in ... azure chiffon 😬
- Get your colours done (I know you said you suit bright/primary colours, but a lot of people - unless they know their own colouring very well - are surprised by the outcome);
- Book yourself an appointment with a stylist to get an idea of shapes & lengths that suit the new slimmer you (not necessarily dresses, I mean clothing overall - sleeve lengths, skirt lengths, neckline shapes etc - it'll stand you in good stead for your future wardrobe purchases!). Not sure where in NI you'd go to these days (it would have been Anderson & McAulay when I was still at home!!). You could post a separate thread asking for recommendations?
If you're petite & busty, ditsy florals will fade into the background/look too casual or frumpy. But large florals will swamp you. I think you're best to go with a single colour of dress (or suit/separates, which others have suggested & would work well - but I think you're set on a dress, aren't you?!!).
A September wedding on a little Greek island ... it'll (almost certainly) be blue skies & sea & sunshine & a bit of a breeze. So something in a single (not necessarily primary, unless you're sure it won't overpower your skin/hair colouring) maybe bright/rich or what I'd call a strong pastel, like coral, colour - & something that's not stiff (like some of the ballgown-type dresses posted) but silky/floaty? No hat!!!
And in a colour that won't get you confused with the bridesmaids! Doesn't have to be a stark contrast - it could just be a stronger version of the colour they're wearing, say emerald green if they're in pale leaf green. Mainly - think of how you want to feel as much as how you want to look? Carefree, relaxed & happy????
Creases do show up more obviously in plain not patterned fabrics, so I'd choose something that either doesn't crease too much/where any creases fall out easily, or it doesn't matter too much because of the shape. Unless you're wearing a really tightly fitted silk dress with tight sleeves, I don't think sweat should be an issue at all (Mitchum extra-strength stick, not roll-on, is your friend!)?? Lots of sleeveless/halterneck dresses posted - personally I wouldn't go for that unless my arms were quite toned (mine used to be, but aren't now that I'm fully menopausal - & shockingly lazy!!). But there are lots of short floaty/puffy/angel sleeve options that will look light & airy & be comfortable.
Finally - start a mood board of what you think you like & might suit you! And if you do get your colours done/see a stylist - take it along/send it to them so that you can come to a mutual agreement about how you want to look & what suits you.
Good luck!!! And keep posting!!