Recommendations for lightweight, high volume, waterproof backpack for commuting?

Hi all,

For over a decade, during the wetter days I've wielded the Ortlieb Messenger Bag. I carry a decent amount of stuff in it (laptop, notebooks, shoes, work clothes, snacks, spares) and fill it up 3/4s most days. I love it for its bottomless capacity, but it's quite wide which obstructs my view and acts like a sail in strong winds.

Can anyone recommends something that's

• Lightweight (1.5kg or less ideally but 2kg fine if the straps are good)
• Waterproof
• Has a one or two compartments for my laptop and small things like keys
• Isn't too wide and doesn't obstruct my view
• Is under £150 and available in UK (max £250 for something exceptional that's multi-use e.g. I can use it for weekly shopping too)
• Can handle bumpy roads
• Doesn't sit so high as to interfere with my helmet

(Duplicate post from r/bicycling as didn't get any answers there and it's more your r/bikecommuting's specialism)

Thanks!