You sure don't have many options on a nice boat. But on a fishing boat you could almost have a Wood Stove.
I had Diesel and Kerosene (two different boats) which I think are about as safe as you'll get and still be able to afford a heater.
Electrics are really expensive.
The Circulating air part is what makes the heater worth while!
No matter what the fuel.
The Missus might not like the Diesel Idea, but I do!
I never did this, but it was on my mind for 20 years.
The galley stove is the Heater. I was going to put Muffin Fans in all the bulk heads so the heated air was circulated slowly and quietly.
As a Safety feature, something gone wrong would smell bad and wake you up.