Really, anything that isn't an aqua soil or calcium based that you find on your LFS shelf will work. Regular Estes aquarium gravel, sand, Flourite, Eco Complete are all good choices depending on your set up and what you want to keep (both plant and animal wise). Then there are blasting and pool sands and other gravels not marketed for aquariums that will work on a budget. I've grown hardy plants well in each of those and none will alter your parameters. Strong preferences from people might be incoming, but honest to goodness they all will grow plants. I could debate minutiae as to what I lean towards and so forth, but pros and cons aren't major among inert substrates for basic plants. Some fish that feed off the bottom (Geos, dwarf cichlids, cory cats, etc.) require sand, some plants grow poorly in anything compact like sand, so you will need to cater your wishlist accordingly but generally speaking you don't need to purchase anything special. Welcome to TPT!