even if it is natural light, the key to high-fashion looks are generally not the lens but the light (and occasionally, the format, and the setting, and of course the models...) the 50/1.4 is optically really excellent; it is sharp enough wide open, and very sharp stopped down to f/2, which is an excellent working aperture for fashion in a certain style (most fashion shots are actually made at small apertures, but f/2 also works) for your fl and crop camera.
it is unclear to me what you mean when you say 'crisp image with blurred edges'. that doesn't make a lot of sense. i assume you simply mean a fast lens which can give you a narrow depth of field, but perhaps you mean a lens that will actually vignette and is less sharp at the edges of the frame. (in which case you should take a look at a lensbaby.)
if you want to step up from the 50/1.4, the 50/1.2 is better for this sort of work, but it takes practice to use it well and it will not make a night-and-day difference; the 50/1.4 is already good. but the f/1.2 does have better bokeh, and resists flare much better, so you can shoot into the light when you want to, which you cannot do with the 50/1.4.
if you genuinely do mean 'fashion' and not portrait work, then the 135/2 can be very useful, though it is better for this purpose on a ff camera than on a crop. it is also easy to get good results with it, though you'll need plenty of working distance (and it is better for headshots than full body).
what would probably be even better for you would be a 35/1.4, which permits you to still separate the subject from the bg, yet provides easier working distances for full-body and environmental portraits (esp on a crop camera).
but if you really want to make your portraits and fashion look professional, then you need to work on lighting. go over to the strobist website and read their intro sections, look at the examples, and you will see what i mean. you can also make a big difference for not very much money, if you simply buy two manual flashes (look for recommendations on strobist). if you have the money, you can go ahead and get two 580ex's instead, which makes some things easier, though soon you'll end up doing a lot of it on manual anyway.
if you still want more advice, try uploading some samples of your work, and point us to a couple of examples of other people's photos that you like and want to be able to match.
sometimes you don't even need a flash to give your photos that lighting-designed look, if you pick where you stand carefully:
