I just got a "One Bag" from Patagonia, in black. It looks good
enough to carry (in shoulder-strap mode) with a suit (for my
purposes), but has a bit more capacity than a typical briefcase.

It has foldaway rucksack-type straps (not as good as a proper
daysac, but better than the shoulder-strap) and the design gives
you a decent-sized compartment for briefcase-type things (papers,
moderate-sized laptop) separate from the larger "overnight"
compartment.

It seems very well made, though I haven't used it much yet.

(I have no connection with the company).

HTH,

eeph