I've worked in indoor air quality for three years and I'm not aware of any products that capture CO2 below the industrial scale, unfortunately. If you come across anything, I'd love to know!
I've tried the indoor plants approach and tested CO2 levels with Kitagawa tubes, and all the data showed was when the HVAC system was running... There are already lots of plants outdoors, and they're lower-maintenance there, so it's worth checking whether your HVAC system could be doing its job better of bringing outdoor plant-enrichened air to you.
- Are the filters clogged? Houses sometimes have a 5" filter hidden in the unit in addition to the return filters.
- Are the coils dirty?
- Are the vents open?
- Are the ducts insulated and in good repair?
- Are the filters the right size and MERV rating for the unit?
- Could the unit be upfitted with a filter that has more surface area, so that it restricts the airflow less? Going from a 1" filter to a 2" or 4" filter can increase the airflow. If not, look for a filter with more pleats per inch.
If you've got great ventilation - or no authority over the ventilation - and you're still experiencing poor indoor air quality, a HEPA air cleaner with carbon can't fix CO2 but it'll get most other contaminants.