You could buy a PC2- 17-4 adapter and install an aftermarket radio. Then you could have Radio, Aux and Bluetooth connectivity with the right 3rd party system. Most third party radios come in a standard size and shape that fit nicely into that small blank cubby hole below the CD/Tape player in the Yaris dash (and most other Toyota models of this era).
This is the adapter that converts from the Toyota/Japenese standard plugs to the more uiversal/Europe standard: https://www.amazon.co.uk/Autoleads-PC2-17-4-Audio-Harness-Adaptor/dp/B000XUQZ4M/ref=sr_1_1?ie=UTF8&qid=1523368214&sr=8-1&keywords=pc2-+17-4
This is then "Amazon's Choce" aftermarket radio, though I'm sure you could Ebay one for half the price if you're on a budget.: https://www.amazon.co.uk/Kidcia-Single-Din-Bluetooth-Receivers-Receiver/dp/B06XRDWB1W/ref=sr_1_6?s=electronics&ie=UTF8&qid=1523368533&sr=1-6&keywords=car+radio
Here's a good guide I found: https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiC2a-476_aAhVFVRQKHcAuA_EQjRx6BAgAEAU&url=http%3A%2F%2Fwww.funkymotors.ie%2Fblog%2Ffitting-a-cd-player-to-toyota-yaris%2F&psig=AOvVaw1z9xLgaPc2FaRYzTwwCxKd&ust=1523455263388531