I think if I had to do it and I really didn't want to attack a real upholstery job, I would just cut the fabric and stitch it on piece by piece...not to the chair but say put the front fabric on the upper part and cut it to fit maybe wrapping it to the back and then cut the back fabric and blind stitch the two together with them in place over the chair..

I would make two separate pieces. A seat cover with a skirt or ruffle that has ties underneath to secure it to the legs, and a slip-over back cover that has split side seams with ties for securing above and under the arms. Whatever the choice, you should attach some kind of non-skid material to the inside of the seat cover to keep it from sliding around on the leather. This shouldnÂt involve more than basic sewing on your machine. Hope this gives you some ideas.

thank you both for the ideas. i really appreciate it!