[Closed] What Pannier bag to replace Courier bag?

I know have a longer commute. Previously I would fit my laptop, D-Lock and gym kit into a courier bag on my back. In an effort to not arrive at work with a sweaty back, and because my old commute didn't have proper rack mounts, I bought the Topeak MTX pannier system, but the largest bag isn't really suitable for my needs.

I now have a bike with proper rack mounts. What I'd like is to have a bag with the same size/pockets as my old largish courier bag that has a shoulder strap with a secure rack mounting system.

Any recommendations?

Cheers,

Paul