Need help

[wellcraftv20step]

Morning guys, I need your opinion on a real important matter. I moved my 84 year old dad into the (14 x25 ft, 7 ft 2 inch ceiling) den in his house it has one step up to the front door instead of the 12 total steps in the upper part oh his enormous split level home. It has a full bathroom on this level, only draw back is it happens to be the only part of the house that's on a slab. I am looking for a heater, electric I guess for when the piece of crap Navian tankless boiler goes on the fritz as it does every year! Theirs like one guy in 2 county's with enough knowledge to work on this thing and it sometimes takes days to get to us. So I need an electric heater to heat the space god forbid!!! I have read about many different units . if you guys have any recommendations it would be helpful ,Thanks