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You could use denim and corduroy with warm and natural batting.And cotton velveteen.
Or get old wool garments (if you can) - wash them - wash colors separately in case some are bleeders - and then cut them up.
Can you find an army blanket? Those are super warm and super heavy and make a great batting.
Life, Liberty, and the Pursuit of Fabric!
I would keep as close to the picture he likes as possible. If you use corduroy or corduroy and denim with a flannel backing, it will be heavy with a cotton batting. Keep it as easy as possible for him to wash. The picture you show reminds me of a grandma quilt. If possible, don't make the rectangles smaller. It will spoil the look he likes.
Wonderful quilt in the picture. It looks like old shirts cut up for the blocks. I buy shirts from thrift shops to make these kinds of quilts. A thrift shop blanket would be great batting and I would back with flannel.
Retired USN Senior Chief
I think I would do the simple blocks like in the picture and use a double bat of cotton (bottom) and then wool with maybe a flannel or nice muslin backing. The double bat will be heavy enough for him and plenty warm too.
I'd use the long arm to tack it down and then tie it. I've tied 2 t-shirt quilts and it can be a bit of a pain---have a pair of needle nose pliers to pull that needle if it get's stuck.
Or you could just machine quilt a grid pattern and then tie about center of your blocks (or every other if 6" of smaller) and it would be that tied quilt but also have a machine grid stand up to the washing and give you an easier quilt to tie with.