I've been looking at some dog sweater patterns available on-line, looking for an easy one for you. I don't know how big your dog is but this one comes in several sizes. LINK
I know some patterns are hard to understand because they are made in the round and you make holes for the legs, etc. This one is real simple. It does require sewing up, but both pieces are explained and you sew they together to form the leg holes. Looks easy.