It's harder, and probably never we'll have an private communication on Nostr like we have on Simplex. It leaks more metadata and the IP addresses are exposed for the relays, sure, VPNs lke yours and Tor routing can be used to solve this, but one mistake you make, an malicious relay can explore. I can say there is a possibility to in a near future,  Nostr npubs databases information like IP addresses can exist.
Yes, there are nostr clients like Amethyst that now uses Tor network by default to protect npubs real identities, but it's not enough, even when you see the nostr:nprofile1qqs9ajjs5p904ml92evlkayppdpx2n3zdrq6ejnw2wqphxrzmd62swspzemhxue69uhhyetvv9ujuvrcvd5xzapwvdhk6qgdwaehxw309aukzcn49ekk2qghwaehxw309aex2mrp0yh8x6tpd4ehgu3wvdhk6ynf30t don't do this at the moment, you have to setup manually your proxy using orbot for example 

 SimpleX Chat have their on internal private routing solution. And to finalize SimpleX is less censorship-resistant, and Nostr is more censorship-resistant because of the design and the number of relays, like Torrent. Both (SimpleX and Nostr) can be self-hosted, but SimpleX is decentralized and Nostr distributed