Quilter's Dream has a heavier weight cotton that I've used. It still quilts up quite well.

I like to use wool for warmth. I think wool batting and a flannel back probably denotes warm and heavy.

Quilter's Dream...the green one made from recycled plastic. It's a very light green, has excellent warmth factor, good drapability and very minimal (if any) shrinkage so your quilt will not look as crinkly as with a cotton or cotton blend. It's very durable but soft. Check the cost against the others mentioned. It is not heavy, though. I wonder if your relative thinks heavy equals warm? The older I get, the less weight I want. But to each his own...enjoy the search for the perfect batt.

Reminder, many people don't realize how warm a quilt can be. They just think of it as cotton - like a sheet. I think the more important part is that they want it heavy. I know a lot of folks like that 'weighted' down feeling when they sleep. This would make me want to use a W&N rather than a poly.

Do you have to check if someone is allergic to wool before using it in a quilt, or is the sleeper "protected" by the backing?

I would opt for a double layer, W&N on the bottom (next to the backing) for weight, and Wool on the top for added warmed and definition to your quilting.

I am not a batting expert, but the quilts I get the most "warm and cuddly" comments on are the ones I have backed with pre washed flannel.

How big is the quilt? less than 58" wide, you can use fleece as batting and back. That makes a heavy, warm quilt.

Ditto on using fleece. It's warm, warm, warm and works well as batting.