Please forgive my ignorance...but what would an average person's knife or dagger have looked like in roughly 1250? Would a seax be appropriate, should it be more like a rondel dagger, or a double edged blade with a more sword like cross guard, or...?

Thanks!

Here is a good discussion of some early daggers that might help with the context just prior to your period to help see how things develop.

Early Dagger Thread

Of course for this time period probably the most referenced chunk of medieval art ever is the Maciejowski Bible

I would guess there are some more threads as well if you spend some time searching.

Best
Craig