Pile up the stones and set up a dry stone wall in front of it

We do not have drainage, however, our wall is built with mortar, not a dry stone wall. Between the soil and the wall, a thick layer of Styrodur was applied to distribute pressure. I relied on trained masons for that. We brought it anyway, because honestly I have no idea how to cut sandstone. You need a frost-free foundation.

I quite like such stones:

My only note is that the (linked) "stones" are made of concrete, so only muschelkalk appearance.
If dry stone wall, then please natural stone; for example, we paid 175 EUR net / ton for German graywacke (+ considerable freight though): one ton is about 1 Euro pallet stacked, yield about 2.5-3.0 sqm/ton, longest edge about 40 cm. But there are also larger ones, presumably even cheaper then.

Or you try it at construction sites. We were also rolling in money. From the terrace excavation, we got some nice big natural stones for building walls. Free for them, no disposal for us.