Impurity on one's shoes

It was raining outside, the sole of my shoes were wet, they touched the top part of my other shoe. The shoes are made of absorbent cotton material. I understand that doubt cannot uplift certainty. But I know that I must have stepped on some kind of najis some where so I think the top part of my shoe became impure, but even if I did there was no trace of it. Also before I stepped on my other shoe I walked for a bit on wet ground, would that have cleaned up the sole of my shoe? I suffer from waswasas as well.