Sadly I just have the big boobs and not the longer legs, but my experience is that the chance of finding a dress that fits all parts of you right is only slightly greater than winning the lottery. I have had two, perhaps three really good ones in my whole life. And they were bias cut, so a bit more forgiving.
As a result, I almost always go to weddings in a skirt/top combo so that all bits fit properly and people can see that I actually have a waist!
Hi. I am a similar shape (without the longe legs Earlier this year I bought my favourite ever dress from Hobbs. Sadly I can't find it on their site. It was a shift dress which is a shape I normally avoid, but there was something about the way it was cut (pleat givein extra fabric from the neckline) that made it perfectly. If there is a branch near you I'd try going there. The assistants alwasy persuade me to try things that I would never have chosen and they always seem to get it spot on.
The other shop I've had luck with lately is wallis. Their dresses/tops seem to be cut for curvy ladies at the moment. Again they have some lovely shift dresses (on the sale that are worth a try (free delivery and returns).
There is a Boden maxi dress in jersey on the sale site which is very accomodating to big bosoms. I got a '16 long' just the other day - must have been a return but there were some 14s yesterday. I think it is £36 and I really heart mine.