Crank type for an old peugot
The easy solution is to rip out the old bottom bracket, put on a modern JIS/ISO bottom bracket. Velo Orange makes some with french threading and threadless (if the threads are stuffed). 

Then find your favorite square taper crankset and put it on. 

Keeping cottered cranks is extra work since the "right way" to do things with cottered cranks requires a bunch of tools nobody has anymore.