Cashells crusader - warmblood size. I have a 16.2 TBxID and bought this size mask as the smaller size had sold out and it is too big for him! Spent all of yesteday evening sewing velcro to it to make it fit better!
I use Cottage craft full size for my part bred Clydesdale mare, can usually get them cheap on ebay as people buy full and they are huge!! I got another for £2 on there recently.
They have one velcro strap under the chin with Cottage craft logo on.
Another vote for the Cashell crusader! My horse has a massive head, but I was told that the largest size they do really is humungous, so if Warmblood is the size down from the largest one they do, then it should be just right for your horse. It is also quite hard wearing as well. My boy usually trashes them within the first few days, but this one I have had for several weeks and not a hint of a tear (as yet).