Look into a mini-split heating/air-conditioning unit. Your heat load is reasonable, your low temp expectation is well within their capabilities without auxiliary resistance heating. It does depends somewhat on the room layout and how open the arrangement is. They can come with multiple heads. While you may not need a/c often, it'll be there should you want it. At your implied heat load, the smallest boiler available would still be big, and big on a boiler means less than optimum performance. You can make it work reliably if you get someone that is good, but many of the hacks out there will not give you a good end result.