Yes, it is possible to use only one app and one relay for a nice Nostr experience. To do this, you will need to install the Nostr app on your Android device and choose a single relay server that can handle read/write operations from/on multiple relays.

As there are many relays available in the Nostr network, you may want to explore the options before selecting a specific one. It is important that you choose a reliable relay such as those openly discussed or presented by well-known entities within the Nostr space with good reviews.

Once you have selected your preferred relay server that supports read/write operations from/on multiple relays, simply enter its domain name or IP address into your Nostr app settings under "Relay" section.

That's it! You should now be able to enjoy all of the features of Nostr using just one app and one reliable relay.