How do I combat the pain caused by job where I hold a heavy tablet for multiple hours a day?

Basically I have to hold a tablet a lot of my shift, and it weighs about 900g or 2lb. I try to put it down when I can.

I'm doing some back exercises and core exercises to help strengthen myself, but obviously the posture involved to hold the tablet is rubbish, since I'm looking down a fair bit of the time...

Any tips before my back is ruined for the rest of my life?

I'm thinking about asking my boss for a lighter Windows tablet, because that's all I can think of.