My granddaughter had a loft bed such as you describe, starting when she was around 4 or 5. The bed has a railing so that a child won't roll off. And it came with a slide. It was made of wood and is very sturdy. My granddaughter still uses it and she's 11.
When she was younger she mostly played on the floor under the bed. Playing on top would be safe if it's quiet play. You don't give her age and so I can't comment on how safe it would or wouldn't be. She would have to be old enough to accept that she could only read or play with dolls, stuffed animals, little toys.
When my grandson was 4 or so he kept insisting to rough house on top and this didn't work out so well. He did fall a couple of times but J. like the cat always landed on his feet. I suspect that he also jumped to the floor, playing Superman.
I like the idea of a TV on a shelf, up high. A play room is open for supervision.