Plural of "fleece" when referring to fleece jacket
Solution 1:
If you write fleece to mean "a jacket or other garment made from a soft warm fabric with a texture similar to sheep's wool," then the plural is fleeces; if you are asking the plural of fleece jacket, that is fleece jackets.
As fleece is also used when talking of a jacket made of fleece (whatever it is sheep's wool, or the soft warm fabric similar to sheep's wool), there is no need to say fleece jacket.