Hi @FATEdestiny,
Thanks for your invaluable suggestions.
I have seen economy ranges at ASDA and Sainsbury's and they don't seem to be for work or evening wear. I checked out Jo Browns and it's very casual, most dresses go upto 20 and are sleeveless. I did a survey with plus size women and most of them said that prefer sleeves or option to have sleeves/lengthen them as they feel they have flabby arms. Actually I also prefer sleeves as I am quite hairy in the underarm area and not always waxed.
Customized dresses definitely won't cost £200. It costs that much in gorgeous couture because they do very red carpet dresses. If I can get the volumes, it would cost 50-80 pounds. A simple dress at most high street mid-range brands (M & S, Monsoon) costs around this much or more. We pay so because it's a big brand, has brick and mortar stores and have a lot of inventory. We pay for the brand name.
I am actually not plus size but I also fluctuate in sizes. A good solution would be to have few (1-2) inches margin left in the dress. I find it very difficult to buy in standard sizes as I have small breasts. If something fits on the hips, it is baggy on the chest. For my wedding, I couldn't find a readymade dress in London, and customized would be unaffordable (1500+). So, I ordered it on lightonthebox.com. It was customized, I entered my measurements, height etc and when I got it, it was exactly my size, all for 300 pounds including custom duty. Anyways, customization is very valuable to be because I am short so normal clothes in the UK are too long for me. Petite ranges have very little variety. If there are 100 pieces for regular sizes, there are 6 in petite.
I have a feeling that you're very young ( envious :) ) so you can get away with any length, casual clothes, sleeveless etc. Also, women start caring about fabric and details once they reach 30. In corporate offices and day events, one needs fitted structured dresses. One colleague of mine also complained that almost everyone in central London is wearing M &S which can be embarrassing if you run into someone wearing the same blouse.
Thanks for telling me about the fluidity in sizes though. I would think about it and find more solutions, but trust me it's a problem for everyone :) Plus size designer wear (Navabi, Anna Scholz) despite the very high prices, are doing exceptionally well in Europe, so women must be buying those. Have you tried ASOS curve, many people have complained it's polyester.
I have attached some pictures of dresses that would look good with customization.
And this is the kind of ethnic print and high quality cotton I was talking about.
www.anokhi.com/photos/photo_archives/bukhara.html
I am in London now but I anyway plan to start this in India as plus size fashion is almost unavailable here.