For our sleeper work we dug concrete footings and faced the sleepers on to the front of vertical batons which were held in concrete (if that makes sense).
If you are going to have the weight of slope of soil trying to slide back down hill you need your sleepers to be anchored and immovable.
Assuming that is your space I would consider terracing it. Top level, held by decent breeze block and render retaining wall, bottom level flush with the patio.
You could do steps up to the top terrace for veg and etc, bottom level lawned for lazing about.
For our sleeper work we dug concrete footings and faced the sleepers on to the front of vertical batons which were held in concrete (if that makes sense).
If you are going to have the weight of slope of soil trying to slide back down hill you need your sleepers to be anchored and immovable.
Assuming that is your space I would consider terracing it. Top level, held by decent breeze block and render retaining wall, bottom level flush with the patio.
You could do steps up to the top terrace for veg and etc, bottom level lawned for lazing about.