I think we need a tutorial on "Sunday casual" for us older women!

I'm still looking for a CASUAL cover-up for warm weather - coffee at Starbucks, Sunday shopping at Target - that kind of thing.
- I don't really want a cardigan
- I prefer the structure of a jacket (a white denim jacket is too hot)
- I like the idea of short sleeves
- I don't want to look too young or trendy, but I do want to be casual

I just saw this jacket in white in the store. It's a fabulous cut for me, but I'm not sure it's really that casual.
http://shop.nordstrom.com/S/30.....4&P=1

Thoughts or suggestions?