For work, I use the
Ortlieb Office Bag (standard width). It's cheaper than the panniers, and comes with a strap for carrying, which makes a big difference over the rollers. You might need the double wide for yours.
It also has an optional notebook padding insert. Completely waterproof.
Internal dimensions are 29 cm * 39 cm * 8 cm for standard / 15 cm for large.
Might be a tight fit for your laptop, but it seems like the best solution out there. I have the backrollers as well, for touring, and they taper down in width a bit toward the bottom. If you go with that solution, make sure the size is right all the way down.
The office bag is cheaper, but you only get one.... It's a tough choice. I have both and love them both. Would love to hear which you go with in the end.