Personal shoppers Oxford Street

[Umbrelladilemma]

Has anyone had any good experiences with personal shoppers in any of the Oxford Street department stores - John Lewis, House of Fraser etc?
I'd like to buy a few new bits and pieces - specifically a dress for a posh do and also some casual outfits (preferably dresses) but am absolutely rubbish at browsing. Left to my own devices I can spend 3 hrs looking and trying on and still come away with nothing. Or nothing that I really like anyway! Also I'm petite with a short body so end up picking up loads of dresses to find they don't fit. So I wondered if a personal shopper who knew their stock might help me??