I only use Warm and White or Warm and Natural batting and I often piece it to use up pieces that might otherwise go to waste. I make sure both pieces have a straight edge, I butt the edges together and use a wide zigzag stitch to attach them to each other. I've never had a problem doing this and it's not noticeable in the quilt.
I buy it off the bolt as well, and it's 90" wide.