Koni FSD = Stock replacement, not designed to go with lower springs with higher spring rates.
Koni Sport = designed to accommodate lower springs with higher rates. Adjustable.
If you are only looking for a lower ride on a DD then the Coil Overs will be overkill. The main advantage that the entry level Coil Overs you would be looking at (Adjustably ride height) is something you are not even interested in. So the advantage of a CO set up is not what you are looking for and the disadvantage (much more harsh ride due to differences in the design of the part of the Coil Over that attaches to the top of the strut tower) would be less than ideal on a DD. I think your solution is pretty strait forward. Koni Yellows/Bilstien HD and a set of good springs.
If improved handling is a concern then get a RSB if you don’t already have one. The Shock/Strut/RSB comb will provide at least the same increase in handling (if not more) as a set of entry level Coil Overs will.
Basically if you are not tracking your car a lot then Coil Overs are not needed for an MS3. You are not driving so econo s#it box that came with garbage suspension from the factory. Mazda produced a car that handles pretty well right out of the box, so you don't need to do as much work to this suspension to get it right. Save your money for other projects by keeping you mind on your end goal, a slightly lower ride in this case.