Sunon 30mm blowers 5v but will pwm down from 12v if you limit them in your slicer to 30-40% (you can blast them at 12v for short periods such as bridging). I have found they work quite nicely with diffuse airflow but you print and bond ducts to them if you wish.
No loss of print volume as they sit under the effector. Brackets I can put on thingiverse, just bond fans on with superglue/ca glue.