Josh, welcome to CF
Isn't the fuel tank
behind the engine
space on a Sigma 33? You will also loose some of the cockpit
locker if you tried to fit the berth across the hull
We have a small double berth in the stern, but if you are looking for Beneteau center cockpit
style stern cabins, then Moody 333 or 34 perhaps,, built by the same yard that built your Sigma.