Bluboo S1 Headphones
Bluboo has opted to completely remove the standard 3.5MM Audio port for the Bluboo S1, they also did the same thing with their Bluboo S3 phone so the headphone options stated here are applicable to both.



Bluboo S1 Headphone Jack Alternative
If you already own a Bluboo S1 phone your seller probably sent you a Type-C to 3.5mm headphone adapter which does the job of the standard 3.5 mm headphone jack so you can use 3.5mm headphones and other 3.5mm audio devices like the 3.5mm speakers with he Bluboo S1. Don't have one or need a spare we have options here   
Bluboo S1 Headphone Adapter


Wireless Headphones
Bluboo S1 phones use Bluetooth 4.0 which although not the most energy efficient form of Bluetooth gives users a wireless option. A minor con is that wireless headphones also have energy limits, this flaw is diminished in Android 8.1 because you can see the battery level of devices your Android is connected to unfortunately Bluboo S1 Wireless headphones users will not benefit because it runs on Android 7.0 Nougat.
Wireless headphones offer greater freedom of movement and if those headphones have a mic like the ones on display here you can not only listen but also talk more freely.
Bluboo S1 Wireless Headphones





Headphones That Can Be Used Directly With The Bluboo S1
Last but not least you can simply use Type-C headphones that can be directly plugged into the Bluboo S1, as I mentioned earlier these options are applicable to both the Bluboo S1 and S3 the Type-C headphone displayed, these headphones also feature mic as well.
Bluboo S1 Type-C Headphones