Help please to find a smart summer coat!

[ChoclolateOrange]

I am looking for something that I could wear over a dress to a summer wedding on a cold day or to the races. I've had a look at the usual suspects in the concessions in the department stores like Jigsaw, Reiss etc, as well as M &S, H&M etc. I need something simple and plain that I can wear for years. I dont want a trench and I dont want anything in a cocoon shape. I am 5'2 and size 12. I would prefer not to spend more than £150. I would quite like a pastel or neutral colour and definitely nothing patterned. I may be searching for the impossible.....Oh, and I don't want to look like a mother of the bride with anything satin or shiny!

Thanks in advance!