Townes has a new Baker fleece and also got a waterproof turnout for Christmas. He normally takes an 80 but his Bakers are 76es.
If your horse is muscular, maybe just go down 1 size, but if its a taller, leaner type maybe go down 2 sizes. Townes is a solid bred Paint, almost 16h, leggy & lean, not much chest. They fit him perfectly.
I actually am really happy with both of his Bakers. If he's sweaty from a ride or caught naked in the rain, throw the fleece on and he's dry in minutes. The fleece absorbs like a sponge.