I have yet to find a platform pedal that works without some sort of retention. A lot of them will tear up leather soled shoes as well. Are you against toe clips because you don't like how difficult it is to get into them, or that they tend to scratch up a good shine? Half clips can make access quite a bit easier, and MKS makes ones that have leathers on them to minimize scuffing of shoes. I know Ben's Cycle sells them, as I imagine do others. Power Grips might be an option for foot retention too.

As for platform pedals, the MKS GR9 or GR10 might work, if you have clips on the front. The GR9's are narrow though. I have some VO touring pedals that I really like and work really well with flexible soled shoes. All these pedal have a bit of traction to them, but not aggressive enough to chew up leather soles.