I think the OP has already purchased something, but I was going to suggest a Baker blanket - the “double” heavier weight one. Easily washed, but I don’t put them in the drier - just hang to dry… And I had D’s put on mine so I could use leg straps.
As an aside, I have an ancient (20 years old at least) Schneiders Dura Nylon Tekno-Fleece blanket, but mine has an open front and bias surcingles as well as leg straps (removable elastic snap-on ones), Unfortunately, they don’t make it any longer. It lasted well until a couple of years ago when the nylon started fraying at the seams as the fabric is so old. No matter how much I stitch it back together, the fabric just won’t hold together any longer! The only thing I didn’t like about it was the adjusta-fit feature for the shoulders. Both the horses who wore it had/have huge shoulders but neither was broadly built so the blanket tended to be a little large in that area. But after 20 years, it doesn’t owe me anything!
