No reason to switch to Monarchy at this point. It is a war time government, so unless you intend to go to war and stay there, forget about it. It is less productive than Republic or Demo over all.
Demo is a tough government to be at war in and is an optional tech, so I never research it and of course never switch to it. It is meant for peace time players. You must get any war ended in less than 20, unless you have many lux hooked up.
The other problem with demo is it does not come early enough. I want to be out of despotism long before I could learn Demo. Since I distain any religious traits, I an loathed to make more than one switch.
It is a bit late now, but I would almost never head to another landmass if I had not already cleared the contient I am on. That way there is no issue of some border town being raze as there is no one there to raze it.
So where you are now calls for you to concentrate on clearing your contient. The switch to Republic is a possiblitiy, you need to have a understanding of how much WW you have now and how much more fighting is to be done.
You can stay at war with little issue in Rep if you have a some lux.