They're obviously no replacement for exhaust fans in bathrooms and kitchens, but there's a number of ductless energy recovery ventilators that can give you fresh air in your bedroom(s).
Thank you - this could solve a problem in my house. We had CO2 build up in our bedrooms and the only way I have found to ameliorate the problem is to have our HVAC fan running continuously at night to circulate the air in our house.
https://www.buildwithrise.com/stories/ductless-heat-recovery