With the wheel
attached to the bulkhead as it is it seems a high stool is all that will work. The ability to see foward becomes a critical element. Attachment would seem best with bolts attached to backing plates
where the bolt holes were properly sealed against leaks
. Direct mounting to the deck
would probably be a mistake.
You might also consider attaching plates to the deck in that manner and then use a second attachment so the stool can be removed and replaced at will through easily removed bolts into the added plates. This would also allow free access around the cockpit
when the stool was not attached. Making it 100% fixed in place might be a mistake. Not properly secured could be dangerous in heavy weather
. You don't have a lot of space to work with. Something strong tall enough and weather
resistent I would think is expensive.