Instead of “I would have done something”, are both of these versions ok?
I would’ve done something.
I’d have done something.
Grammatically speaking, all the three constructs are correct. The non-contracted first one is more formal. The choice between the other two can be made only by euphonic considerations, i.e. whichever sounds nicer or is easier to pronounce given the surrounding words.
The very colloquial I'd've is not unheard of either.