I have had two sizes of herbags and a Kelly 32 and I wouldn't recommend any of them for a work bag when what it sounds like is you need it to perform tote-like functions.
The Herbag GM is huge and the shoulder strap is uncomfortable if the bag is loaded with heavy things or a lot of things. The canvas will also sag a bit with heavy loads and it makes it look a bit frumpy then. But an insert would remedy this and you could just carry the bag in the hand and reserve the shoulder strap for light days or emergencies. So, just keep this in mind. If you are seriously considering the Herbag, then look for the older 2- in 1 bags because you get more for the money.
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As you have noticed, the 32k is too small and the smaller Herbag would also be too small for the purpose you mentioned for the bag.
So I'd suggest something that is either a tote bag ( Birkin, HAC, gp, double send, etc) or a duffle bag (lindy), or a messenger bag (Evelyne).
To be honest, I'd get a canvas gp in mm size to tote work things with and then get the Kelly or some other leather bag just to carry and enjoy no matter what the function.
The other suggestion I would have is to look at the 32 HAC as a work bag because it is a bit taller than the other Birkins and can also look purse like and less "tote" if you know what I mean. I have one in boxcalf and love it. I don't use it for work but carry it when I need to carry more items than my 32k but want to look professional and not casual (like the canvas gp or other bags). The box calf is stunning and lightweight but I don't know what your workplace is or your lifestyle, so keep these into considerations.
Best of luck to you!