An old Canonet 'D' Flash is pretty minimum, quite strong, but you'll need a cold/hot shoe adapter with a pc cord, or, try out a Sunpac, like the MX 124, which very adjustable and has a thin pc cord.
The Sunpack is a flat affair, and there are several flash units in that brand that look similar, so you'll have a choice, and enough power for your photo adventures.
The pc cord press fits in a 'U' shaped channel on the side of the unit, but personally, if I could, I'd change that cord out with a heavier line, perhaps even shielded speaker line.
I like the Sunpak for use with my Minolta TLR, as it folds flat along the camera's side and does no have an intrusive 'head', which makes it a perfect small carry.
IMO