How do I cope with isolating work that sits me all day?

The work is steady, and you are grateful for that, but sitting alone in a cab hour after hour does a quiet kind of harm, to your body from the stillness and to your mind from the solitude. It is easy to dismiss because nothing dramatic happens. But slow damage is still damage, and you are right to take it seriously. Because it is slow, the fix is slow too, made of small habits repeated. For the body, use the breaks you have. Get out of the cab, move, stretch, walk a little, whatever loosens what the sitting tightens. A few minutes each shift adds up over the years and keeps the stiffness from settling in for good. For the mind, the isolation eases when you build small threads of connection. A word with the crew at breaks, a call to someone on the drive home, a habit that puts real people in your day. You do not need constant company. You need enough that the quiet does not turn heavy. Pick one thing, moving your body or reaching another person, and start it on your very next shift.