If I were you I'd go to my local electrician store and explain them what you want. I haven't ordered a thing on the net for that. You can see what you'll be buying.
You can buy the din rail you need, they'll cut it for you. The socket for the relay or perhaps a din relay. The power outlets (mine are Niko, a bit expensive but good). My relays are mechanical.
You'll have to tell them you'll be using 5V for the relay, the load... Perhaps a small case to hold it all...
The only thing they won't be able to sell you is something like the
https://www.winford.com/products/brkub1f.php . I do not have such a thing but in my mind that's what you need. You could also wire the usb power directly to the relay.
If you are uncertain you can just buy their proposed relay and see if it switches using the usb power? If it doesn't work out there's not much lost.
That's what I would do. I'm not an electrician at all but I always got good advice and sometimes a wiring diagram in the store.