It is probably worth looking in any of the shops - I like New Look which is very reasonable. Etam, Pilot, Miss Selfridge & Warehouse all have a lot of layer-y clothes too. If you stay in the York area, it is worth a trip to Harrogate as they have a big TK Maxx, New Look and MK One which have the sort of things you suggested, as well as a lot of smaller, interesting designer shops.