In reply to Hobbit Helen:
Exped do short length mats and sleeping bags, with a wide choice.
Lightwave do shorter sleeping bags
PhD mentioned above do both standard short versions, half bags and made to measure.
They are all at the premiere end of the market.
The next problem will be finding anyone who stocks so you can try out, note PhD are direct to customer only with no retail outlets
Your final choice is to find on ebay, or here second hand on UKC a cheap sleeping bag, hand-wash it and chop it, assuming your sewing skills are ok ish. Down normally degrades most around the head & chest (the bits you would chop off), while the rest of a bag is normally is good nick, so a bag a regular user wouldn't look at, or would assume was worthless due to degradation, might be a bargain for you; particularly if you are also on the slim side.
Post edited at 12:01