Biggest issue with the monitor is the stand is not height adjustable, which could mean you are looking down too much. Best get an adjustable stand or a riser arm to adapt more to how you want to sit etc.
Cant help on the back support, aside from a proper chair. When I injured my back I was told a towel folded at the rear of the seat base was good to rotate pelvic forward slightly for sitting. Guess it depends what pain you are experiencing. I just purchased a home office following a 2 week stint of working on the dining table & the change was immense!