A bit late to the party, but in case you track replies, I can recommend the Avantree "Audikast Plus" device. Negligible weight, it gives you Bluetooth capability for two simultaneous headphones as long as you can plug it into a 3.5mm jack. I have been carrying it in my travel bag for years (the current model looks identical but is Bluetooth 5.0 compatible) and it makes our flights and hotel trips a delight (sound experience, I meant).