Answer = Neither
Best long term approach:
- You buy a quality box spring and leave slats as is. In the US they are practically giving these things away not sure how it is in other countries. Box spring will disperse weight to edges. Removing the spacers will degrade your bed as it looks like the spacers are connected to both sides - so they are not actually "spacers" but actual fasteners!
- If you do not want a box spring and you are OK with an unsupported mattress the next best option is to buy a 3/4" piece of plywood and cut it to size.
Neither of these methods needs more slats, which by adding more you are taking away from the structural framing of the bed. I highly adviceadvise not removing the "spacers".