What is the cheapest way to make well water with 800ppm TDS suitable for bathing and washing dishes?
There are three basic non-snake oil devices that one might use: sediment filter, RO filter, and water softener.

A sediment filter doesn't remove dissolved solids.

An RO filter is not suitable for high volume uses like bathing, dish-washing and clothes washing.

A good water softener is the right product for your needs.

But you might add an RO filter in the kitchen to supply water for drinking and cooking also.