Hello and welcome
Any pics?
In my opinion is better wait the end of winter/start spring to add fishes...just useless to put em now that the temperature will fall.
Not any products, but only add more plants and "cover" the water surface with floating plants or lilies(or similar plants)(like 60% of the surface) to fight against the weeds/algae reproduction.
With right balance of these and fishes population you could stay w/o a filter.
And, coz some here and me too are promoter of that, if you got space you should make a "bog filter" that is more efficient than "only plants".