Big question....why? Not trying to be a jerk just trying to figure out what you expect to accomplish. Generally, hydraulic steering doesn't make a lot of sense unless you're dealing with a much larger boat with larger rudder loads (50'+) or trying to operate multiple steering stations as you would on a boat with a pilothouse and helm in the cockpit. Include an autopilot and you're talking helm pumps, hoses, multiple connections, reservoirs, actuating cylinders, continuous and reversing type autopilot pumps...reversing solenoids......possible fluid leaks, seals to wear out.....
I'd stick with your existing steering system and if you want a below deck autopilot, you should be able to fit a 12v linear drive unit. If you can't, then you could go to a compact hydraulic drive unit with the combination pump/reservoir. Not as simple and probably not as trouble free as the all electric system.