Generally people don’t order readymade Flute having Thumb-hole. I suggest you visit a nearby Flute maker with your existing bass Flute, discuss together your playing style and resolve the thumb-hole. Its a matter of not more than 15mins.

And in near future, for ordering a new Flute( with thumb hole ) visit a maker in person or courier your existing thumb hole Flute to the maker.

Because even a slight deviation from the natural thumb position may lead to muscle pain in a period of time and more importantly the notes may start sounding sharp/flat because thumb is naturally trying to rest on the given thumb hole while compromising the blowing angle.