are you going to buy it in person or online? if in person, maybe they have a back protector in the shop you can try and fit in there and see if it works?
otherwise, the protector you linked to looks like it would be more than comfortable. I know Erok81 has a Bohn back protector (with the straps) and he seems to like it. Doesn't come on often anymore but you might PM him and ask him how he likes it.