We used to heat ours when north with kerosene heaters. We had a smaller one that was inadequate then opted for larger. The smaller one was cylindrical and about 8" across and 3' tall. It wasn't quite enough when we were up in Nova Scotia. (We headed south which is the ideal solution to cold weather.)
We bought a shorter, wider kero heater next. The "set off" area (you can't put it close to the wall) was solved via a piece of board the unit was bolted to. Octagon shaped, it gave a wider base (more stability) and allowed us to shove it into corners. The top also made coffee if we weren't rocking too badly.
Have I mentioned heading south?!?
Of course with kerosene heaters you have to leave a window cracked and humidity is a problem. Plus smell -- some folks can't tolerate the odor though there are now additives to cut down the smell.
AND most important of all: congratulations on your new boat. It's a wonderful life. Enjoy!!!