As a soft boot splitboarder with multiple ankle injuries over the years there are a few I recommend. I have stuck with Salomon Malamutes, and like driver x, ride insano, 32 tm2 (which is slightly softer than the others) and the flow talon. Happy shredding.
One thing to consider when trying on boots, is although out of box, stiff boots feel way stiff, they all will break in and have more movement after some usage. Plenty of good deals on malamutes out there.