Yes, if you want to connect 2 pieces of batting, you don't want any overlap. Here's a link to a tutorial I found, and I have used this method:
http://www.modabakeshop.com/2013/09/...g-batting.html
I question that you need to make your quilt so large.... I did a 120x120 quilt for my king size bed, and it's really too big. Looks great on the bed, but is a little cumbersome for sleeping. I guess I don't see why you'd need to go wider to fit your extra-tall partner ... maybe a little longer, but not wider....
Anyway, I don't know about longarmers either. But you could consider a Quilt As You Go approach. I did a king size that way, basically in 25 sections. Here's a picture:
http://www.quiltingboard.com/members...74-326020.html