Both peat moss and vermiculite (yes we sell them) hold water so, if your soil is prone to drying out, they would be appropriate additives. Otherwise just adding compost (we sell composted manure) and some organic nutrients would be all I’d suggest. For nutrients, I’d suggest Espoma Bio-Tone since it contain the organic nutrients as well as beneficial soil microbes and mycorrhizal fungi to help you plants make the most of the nutrients. More on Bio-Tone HERE