For now, some Fitbit watches have Fitpay option which works directly off the watch - similar to Garmin Pay. Check availability by country (for me in Canada Fitpay is pretty much accepted by most banks but Garmin Pay is very limited)
I am using Fitpay and can pay directly from my watch without it being synced/associated to a phone OS. With Google having purchased Fitbit and slowly making changes - will see how long this lasts
Good luck.