Masha,I think this boy at the shelter sounds wonderful and i am 100% sure your Monkey will love having a kitty-companion,once he gets used to him,you already know it can be a slow process,but you'll be amply rewarded when they become friends.
I have 3 males,should have been only 2 but things happen
I also think another male is your best choice,as long as he is neutered.
Good Luck