If the boat has a 140 stat in it your temp may be normal. I find that with a 160 stat in my OMC it usually runs between 155-160 at idle and at most it will touch 175 after coming off plane but then cool back to 160 after slow speed running or idling. Get an IR Temp gun and check your readings, on the intake manifold right under the 'stat housing. This I find seems to corelate closest with the dash gauge reading, usually it's about 10* lower.
About the choke, I have had both the intake manifold heated choke (Rochester) and electric (Holley) my experience with them has been that the intake heated choke takes a long time to open unless you are actually running it on the water, if just idling on the water hose they take forever to open all the way. The electric chokes open almost too fast, they are just responding to the voltage applied to the choke heater and not what temp the engine is actually at (as do the intake heated chokes). You can in some cases convert to an electric choke but if it needs a full 12V to open it, keep in mind you will need to find a terminal on your alternator that provides 12V with the engine running, but zero with the engine off, even if the ignition is still on.
Also if you can get one for your engine, you can put a 160 stat in it, for OMC/Volvo engines that's all that I have ever found and I have not had overheating issues with the 160. Keep in mind that these auto based engines were designed to run much hotter (it 195* stats, so running temps of 195-210 or so are typical). However, in an open or raw water cooled engine which is what most of us have, due to the fact that the cooling water is not pressurized, you cannot run that hot, because you could get localized boiling in the hotter parts of the cyl head (ie like near the exhaust valve seats) if you were running that hot. The pressure cap in a closed system keeps that from happening.
Keep in mind that when we drove carbed cars, a normal part of the yearly tune up was cleaning the choke plate, pivot points and linkage. If they get dirty the choke spring may not be able to open it all the way. So before you change to an electric choke, clean up what you have, and see if that helps it to open.
Personally I'd rather have a manual choke on a marine engine due to the issues noted above, but the available conversion kits are not good quality.