Garlind Mullin

I have a need for a fairly heavy machine thread to be used on veg tan leather. I want the leather to be able to stretch as much as possible after it has been sewn. I have worked with leather on and off for a long time but I am a total novice when it comes to machine sewing. I have a Pfaff 145-H3-6/01. I also want the leather to last a very long time. Any help would be greatly appreciated including information on thread and needle sizes. Thanks in advance Garlind