Pack light and then buy a nice sweater when you're there if you need one. I went to Ireland one year when I was getting reports that the weather was warm and wonderful but became cold and rainy shortly after I arrived. I had a raincoat and a cotton sweater -- not warm enough.
I bought a couple of sweaters in Ireland, one of which I'm wearing now since it's a bit chilly here this morning. The sweaters that I bought were made in southwestIreland, designed based upon local colors (heather, flowers, etc.). I get compliments every time I wear one.
On my recent annual physical, my doctor was wearing a beautiful cashmere sweater; she told me her husband had bought it for her in Scotland.
Have a great trip and please post a report when you return.