Which personal shopper? John Lewis, Debenhams, who?

[BreakfastAtSquiffanys]

I need some help in finding a perfect outfit for an event.
I'm guest of honour, and the style I want is for daytime, not as formal as Mother of the Bride, but heading that way.

Age 60, size 12-14. Reasonable budget up to £200.

Where should I go?
I'm useless at shopping. I know roughly what suits me but I get bored quickly

I can get into London if need be.