This tileset looks very cool: https://stealthix.itch.io/4-colour-tileset
It's the first free 8x8 tileset I've seen that would be a good fit for Solarus. The only problem is that many prebuilt entities need to be 16x16 (including the hero). But you can probably get around this with a bit of hacking in the scripts. It would be interesting to see someone build a tiny game with this.