Great question — a comfortable long sitting bench that keeps a modern minimalist street bench look is absolutely doable: the sweet spot is clean lines plus enough ergonomic shaping that people don’t feel punished after fifteen minutes. I’d focus on four things.
First, choose a seat with a slight contour or a waterfall front edge rather than a completely flat slab; that tiny curve reduces pressure under the thighs. Second, get a version with a backrest and armrests if you can. A backrest angle around 100–110 degrees makes a surprising difference for long sitting, and armrests help people get up easily. Third, combine materials: a powder-coated steel or aluminum frame with warm wood slats — FSC teak, thermally modified ash, or Ipe — gives you the minimalist look but avoids the cold/hot feel of all-metal seating. Fourth, keep the seat height around 420–450mm and seat depth around 400–450mm; that ergonomic bench design supports a relaxed posture without looking bulky.
For ready-made options, I’d look at outdoor street furniture ranges from Emeco, Landscape Forms, or mmcité — specifically their modern bench models with a backrest and armrest configuration. The Emeco Run bench is a good design-led minimalist choice, and many commercial ranges offer slim wood-slat benches with just enough contour. If you're working with a fabricator, specify a slim profile but require a subtle seat curve, a backrest with a 15–20 degree recline, and hardwood slats with rounded edges.
If I were choosing for a public streetscape, I’d pick a wood-slat bench with a black or dark grey frame, integrated armrests, and a slight seat curve. It photographs beautifully, looks sharp against pavement, and people will actually stay there.