Will shopping with a friend bring me back down to earth?

Is shopping an activity best undertaken with an adviser in tow? A burning fashion dilemma if ever there was one, the outcome of which is as potentially hazardous as it may be fruitful.

We all know, after all, that it's all too easy to be carried away by the moment. Even the most minimally minded (or indeed, supposedly expert) woman might, for example, find herself wafting about in a floral-print chiffon tea dress, dreaming of a more pastoral and devil-may-care lifestyle, in which aspiring to be Sienna Miller might be acceptable, or even strangely appealing. She could, say, wear it with wellies. And now, I think I'm going to be sick.

With this, and hopefully somewhat more inspiring if equally unlikely role models in mind, I'm swanning about in a black silk crepe jumpsuit, with a knotted back, dropped crotch and flared legs that are apparently around nine feet long, thinking Charlotte Rampling circa Night Porter, thinking early Yohji Yamamoto photographed by Nick Knight, thinking – basically – that I have to have it, when a friend and colleague, who also happens to be a stylist, states without batting an eyelid and sending me plummeting back down to earth with a bang: "It doesn't look expensive enough and you'll have to wear heels – which you won't. I don't like it."

Somewhat deflated, but ever the optimist, next comes a pair of cropped bouclé wool trousers. "You only ever wear jeans," says she. "Yes, but do I look fat?" I wonder, out loud, pathetically. My friend, at this point, has the sound judgment not even to comment. "You can wear them with ankle socks and brogues. That will work." Sadly, my fleeting desire for brogues covered in crystals is greeted with a tone not much short of derision: "You don't wear clothes that make people laugh."

Finally, I'm back in a jumpsuit again, another one and something I would never – ever – have thought to try on for myself. It's in heavy black wool, boned at the waist and with cropped, peg legs. "I love that! You look really cute. It's space age. It's obviously designer. You should have it." And the miracle here is that I actually love it, too, and so a very special piece (yes, it's that serious) is in the bag.

"You won't be able to wear it if you put on any weight, though," says my friend. And now she's pushing it.