I had a car with just a tape deck. This turns out to be all you want.

I went through two phases:

1. I ordered some type of Walkman-like car kit that came with a portable CD player, glue strips to adhere the CD player to your dashboard, and a cassette tape adapter that plugged into an aux port (on the CD player) and inserted into the tape deck. I'd burn CDs to play in the car that way.

2. I got a Zen Stone, a tiny mp3 player with no screen that was easy to operate by feel. I stored mp3s on it... and plugged the cassette adapter that I still had into it. That was as good as in-car music can get without being voice operated.

They still make the adapters: https://www.amazon.com/Arsvita-Audio-Cassette-Adapter-Auxill...