I'm petite, but relatively broad across the shoulders and largish of boob. TBH I usually buy from a standard range and get the sleeves taken up.
Obviously it depends what style you're looking for and the preferred length (if I want something that has a fitted waist in the right place, I shop petite).
I do go for fairly classic styles to be fair, but I wouldn't say they were frumpy. Jaeger is generally designed for the tall in general IMO, but I've had knee length coats / swing style hip length coats (prob a bit out of fashion now) that have worked well.
I often shop in Hobbs as they shorter in the waist than most shops IME, which works for the vertically challenged. I'm 5' btw, size 10 and 30F.
I guess what I'm saying is - unless you're an awful lot smaller than me - don't discount the normal ranges. My current winter coat is supposed to be mid-thigh, but on me looks like a just above the knee coat dress and I've had lots of complements as it doesn't look 'wrong', just different from when it's worn by someone of 5' 10".
Equally sometimes the more 'traditional' ranges are worth a look. I recall in my 20s when funnel neck, semi-straight cut trench coats were in, I found a fabulous one in Precis Petite, which is not a shop I'd usually consider.
I'd also be prepared to try lots of things on. I used to be very guilty of only trying what I thought would suit me. I think if you're difficult to fit (as I am), then widening what you're willing to try is worth a shot. I was utterly convinced last year that I was buying a coat in Biba that was totally my style. Tried it on and it looked hellish. DP came up waving the coat dress style and I was unconvinced, but it looked great on.