Different ion effect

I need to have the highest concentration of (bi)carbonate ions in a water solution. 


Thus far, my only idea was to use Potassium Bicarbonate (safe and cheap) as it has the highest solubility but it is yet not enough.


I was thinking whether adding both Sodium AND Potassium Bicarbonate, to saturation, would increase the total amount of dissolved Carbonates.
Another solution, which might be more promising is using a complementary salt to make use of the 'Different ion effect' and increase the solubility.


Would any of these options be useful for my purpose? Thanks alot for the help.


