What water filters are suitable for hard water?

The best filters for hard water are activated carbon filters, reverse osmosis filters, or water softeners. However, reverse osmosis filters remove all compounds and minerals from the water, so you would need to remineralize your water to add calcium and magnesium. Water softeners also remove the minerals from the water because it is the minerals that give the water that "hard" feeling.

If you want to save on soap, the best option is a water softener. However, calcium and magnesium are the two minerals responsible for creating hard water, so wanting to retain those while softening your water may be tricky. The best option would be something like reverse osmosis, with the addition of mineral drops.