The weather here has been about the same and I got a 300 gram fill blanket for my 18 year old mare. I leave it on 24/7 unless I work her. She is also turned out 24/7 and a rescue that needs more weight. Since I go to feed her everyday I check to make sure she's not to warm, she hasnt been hot or sweaty under the blanket at all even with it now 40 degrees out. It also kept her warm when we had wind chills of 35 below.