I use pool filter sand often, it's a bit coarser than "play sand" here in the US. But I often like a darker substrate, PFS is often white or pale tan so not my fav. Your tank is small, so don't let cost deter you from what color you like. I've never used it, but Carib Sea Peace River seems like a great choice to me, maybe someday. Larger substrates are harder to plant in & "crap" (fish poo & detritus) can work their way down into it. I bought expensive Eco Complete (not sand, more fine gravel) 20+ years ago & still use it. I like the almost black color.
Soils scare me in some ways. They break down into dust or mud & can cause all kinds of trouble. I've only used old Aqua Soil in an experimental plant grow out tank. I won't being trying it again, although the few plants seemed happy.
Any substrate can work, but bigger sand or smaller gravel is easier to clean & to plant in. Too fine can be a dusty/muddy mess. Don't worry about having "starter" bacteria, like Cass said, it doesn't last. I think I told you I use root tab fertilizers for most plants.
Pick a substrate you like the color & size of & work with it.