We have determined through trial and error and multiple pool builders and designs, that the best way for us to have the ability to swim at our house is by using an Endless Pool (we also went through a variety of other swim spas - Michael Phelps, Arctic, Premium Leisure - and wet-tested all but the Premium Leisure - happy to talk to others about this experience). The reasons are endless that we went this route - but we're looking for year-round swimming with little muss and fuss, no trees harmed in the process, and way fewer historic or permit hoops to jump through.
We're looking at the 15' spa version (15' x 7'7", 2100 gals) which will be above ground on a 4" concrete pad with the 4" thick "hot-tub" cover and the electric heater that comes with it. I wouldn't be opposed to adding some additional insulation somehow, because I don't like the look of the outside of the pool, we'll be doing something wood or something around as much as possible to hide the sides, which could also hide insulation if that helps.
I've asked Endless Pools about using this year-round outside - and have just asked to talk to people in the area that have it outside, to see what type of utility costs we're talking about. Somebody with an Arctic Swim Spa in PA was working with about $60/month extra utility around the year for pump and heating, but I think their spas are better insulated.
Any insight or help to this would be helpful. We could probably end up enclosing it if absolutely necessary, but we were hoping to not have to go that route, at least to start.