Just leaving the suggestion of a specially designed bag for a moment -
I don't fully understand your predicament - there are loads of bags that would take a laptop.
What extra features are you requiring that rule out Sacs a Depeches, 35/40 Birkins, Kellys, HACs, Citybacks to name but a few?
SaD/B/hacs don’t have shoulder strap. Shoulder strap is a must; bag handles have difficulties staying on my narrow shoulder and I need both hands free on transit.
Even K35 looks stuffed with a laptop in it, with no room left for a pair of heels.
For city backs, I personally don’t like the look of backpack over dress/skirt.
Periogirl28’s suggestion is spot on - slimmer but taller version of Victoria/Plume with shoulder strap and a separate compartment for laptop will be ideal.