Dare I say it, you maybe need a dedicated commuter bike?
Do you really think you’ll be wanting to faff about, fit guards and a rack on a cold Sunday evening for the 50th odd time a year or so from now?
Anyway my commuting solution was a klickfix bag for all.my stuff, Whenever I needed to move a laptop (rare these days TBH) I used a 20L drybag lashed to the bars (or left it in a.locker at the office the day before if possible).
The other thing that worked well for a while was a simple beam type rack, that just clamps onto the seatpost, some of those can actually take a full pannier bag, again I just lashed a drybag to the top.