Slightly odd but replacement screws for backing plate of Garmin HRM

I think I'm needing to replace the screws on my Garmin HRM sensor as I think I'll have 1 more unscrewing before the heads are gone...my eyesight is terrible these days so I can't see how small the screw thread is etc.

Does anyone know the dimension of these screws?

Also, I'm hoping I could swap the head from a phillips head to a torx or allen head as I suspect they would last much longer.

Thanks.