https://www.rei.com/product/154226/rei-co-op-650-down-jacket-20-womens

Something like this from REI (REI Coop, Patagonia, etc) -- good quality and good companies, and decent prices this time of year. I've had an REI co-op version for a number of years and it's always warm enough. Also packs really small so it's great for vacations. Also, fuck amazon.

You might be able to find something used from the Trail Hut as well.