I think you underestimate how powerful ceiling fans can be. The highest temperature in Sweden this year was only 36, you would be absolutely fine with a ceiling fan unless you wanted to exercise.
That said, if you are able to get a ground source heat pump, that's awesome, but it's something like 10x to 20x the price of even a really good ceiling fan.
Ceiling (or for that matter any) fans work on your own evaporation. So unless you accept unacceptable levels of humidity or acclimatized to much hotter climate than Sweden and are there for a short time they are not a solution.
Ground source is overhyped and overpriced. District heating and air-exchange AC is still the winning solution.
Well if there's no convection you must be in a vacuum!
But if you mean no forced convection, that's just not the case. You can survive at wetbulb temperatures in excess of 30 C, which means 30 C + 100% RH. Hell, my house right now is at about 25 C drybulb and 18 C wetbulb, which from the perspective of evaporative heat transfer is identical to 18 C with 100% RH, so I should be dying any minute. See you on the other side!
you still have convection even in a sealed room. its walls also do not have zero thermal conductivity so if you don't move, you only have to reject about 100W and that is survivable
That said, if you are able to get a ground source heat pump, that's awesome, but it's something like 10x to 20x the price of even a really good ceiling fan.